#include <bits/stdc++.h>

using namespace std;

int n, k;
string s;

int main()
{
	int t;
	string subseq;
	cin >> t;
	assert(t >= 1 && t <= 5);
	while ( t-- ) {
		cin >> s >> k;
		n = (int)s.size();
		assert(n >= 1 && n <= 1000);
		assert(k >= 1 && k <= n);
		subseq = "";
		int last_pos = -1;
		for ( int i = 0; i < k; i++ ) {
			char smallest_char;
			int leftmost_pos;
			for ( int j = last_pos + 1; j <= n - k + i; j++ ) {
				if ( j == last_pos + 1 ) smallest_char = s[j], leftmost_pos = j;
				else if ( smallest_char > s[j] ) smallest_char = s[j], leftmost_pos = j;
			}
			last_pos = leftmost_pos;
			subseq.push_back(smallest_char);
		}
		cout << subseq << endl;
	}
	return 0;
}