import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.BufferedWriter;
import java.util.Collection;
import java.util.HashMap;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.HashSet;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        meetup solver = new meetup();
        solver.solve(1, in, out);
        out.close();
    }

    static class meetup {
        public InputReader in;
        public OutputWriter out;
        public HashMap<String, HashSet<String>> g1;
        public HashMap<String, HashSet<String>> g2;
        public HashSet<String> s1;
        public HashSet<String> s2;
        public int n;
        public int m;
        public int ka;
        public int kb;

        public void solve(int testNumber, InputReader in, OutputWriter out) {
            this.in = in;
            this.out = out;
            n = in.nextInt();
            m = in.nextInt();
            ka = in.nextInt();
            kb = in.nextInt();
            g1 = new HashMap<>();
            g2 = new HashMap<>();
            s1 = new HashSet<>();
            s2 = new HashSet<>();
            read(g1, s1, ka);
            read(g2, s2, kb);

            while (true) {
                int sz = g1.size();
                String q = null;
                for (String s : g1.keySet()) {
                    if (s1.contains(s) && g1.get(s).size() * 2 < sz) {
                        q = s;
                        break;
                    }
                }
                if (q != null) {
                    ask1(q, sz == 1);
                    continue;
                }
                for (String s : g2.keySet()) {
                    if (s2.contains(s) && g2.get(s).size() * 2 >= sz) {
                        q = s;
                        break;
                    }
                }
                if (q != null) {
                    ask2(q, sz == 1);
                    continue;
                }
                answer("No");
            }
        }

        public void read(HashMap<String, HashSet<String>> g, HashSet<String> s, int l) {
            for (int i = 0; i < n; i++) {
                String w = in.next();
                g.put(w, new HashSet<>());
                if (i < l) s.add(w);
            }
            for (int i = 0; i < m; i++) {
                String a = in.next(), b = in.next();
                g.get(a).add(b);
                g.get(b).add(a);
            }
        }

        public void ask1(String q, boolean last) {
            out.println("A " + q);
            out.flush();
            String rs = in.next();
            if (s2.contains(rs)) {
                answer("Yes");
            } else {
                if (last) answer("No");
                reduce(g1, q, false);
                reduce(g2, rs, false);
            }
        }

        public void ask2(String q, boolean last) {
            out.println("B " + q);
            out.flush();
            String rs = in.next();
            if (s1.contains(rs)) {
                answer("Yes");
            } else {
                if (last) answer("No");
                reduce(g1, rs, true);
                reduce(g2, q, true);
            }
        }

        public void answer(String resp) {
            out.println("C " + resp);
            out.flush();
            out.close();
            System.exit(0);
        }

        public void reduce(HashMap<String, HashSet<String>> g, String root, boolean conn) {
            g.keySet().removeIf(x -> !x.equals(root) && (conn == g.get(root).contains(x)));
            g.values().forEach(v -> v.removeIf(x -> !g.containsKey(x)));
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (this.numChars == -1) {
                throw new InputMismatchException();
            } else {
                if (this.curChar >= this.numChars) {
                    this.curChar = 0;

                    try {
                        this.numChars = this.stream.read(this.buf);
                    } catch (IOException var2) {
                        throw new InputMismatchException();
                    }

                    if (this.numChars <= 0) {
                        return -1;
                    }
                }

                return this.buf[this.curChar++];
            }
        }

        public int nextInt() {
            int c;
            for (c = this.read(); isSpaceChar(c); c = this.read()) {
                ;
            }

            byte sgn = 1;
            if (c == 45) {
                sgn = -1;
                c = this.read();
            }

            int res = 0;

            while (c >= 48 && c <= 57) {
                res *= 10;
                res += c - 48;
                c = this.read();
                if (isSpaceChar(c)) {
                    return res * sgn;
                }
            }

            throw new InputMismatchException();
        }

        public String next() {
            int c;
            while (isSpaceChar(c = this.read())) {
                ;
            }

            StringBuilder result = new StringBuilder();
            result.appendCodePoint(c);

            while (!isSpaceChar(c = this.read())) {
                result.appendCodePoint(c);
            }

            return result.toString();
        }

        public static boolean isSpaceChar(int c) {
            return c == 32 || c == 10 || c == 13 || c == 9 || c == -1;
        }

    }

    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object... objects) {
            for (int i = 0; i < objects.length; i++) {
                if (i != 0) {
                    writer.print(' ');
                }
                writer.print(objects[i]);
            }
        }

        public void println(Object... objects) {
            print(objects);
            writer.println();
        }

        public void close() {
            writer.close();
        }

        public void flush() {
            writer.flush();
        }

    }
}