//Why 860?
#pragma GCC optimize ("Ofast,unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);
#define all(v) (v).begin(),(v).end()
#define pb push_back
#define mp make_pair
#define sz(v) ((int)v.size())
#define FER(i,x,y) for(int i=x, j = y; i < j; ++ i)
#define IFR(i,x,y) for(int (i)=(x);(i)>=(y);(i)--)
#define ff first
#define ss second
typedef pair<int, int> ii;

const int N = 1e5 + 2;

struct SegmentTree{
    int n;
    ii t[2 * N];
    ii OpId = ii(-1e9, 1e9);
    SegmentTree(){}
    ii Op(ii &a, ii &b){
       if(a.ff > b.ff) return a;
       else if(a.ff == b.ff && a.ss < b.ss) return a;
       else return b;
    }
    void build(){ IFR(i, n - 1, 1) t[i] = Op(t[i << 1], t[i << 1 | 1]);}
    ii query(int l, int r){
        ii ansl, ansr;
        ansl = ansr = OpId;
        for(l += n, r += n; l < r; l >>= 1, r >>= 1){
            if(l&1) ansl = Op(t[l ++], ansl);
            if(r&1) ansr = Op(t[-- r], ansr);
        }
        return Op(ansl, ansr);
    }
}st;

int main(){
    fastio;
    int t; cin >> t;
    while(t --){
        string s; cin >> s;
        int k; cin >> k;
        if(k>= sz(s)){
          cout << endl;
          continue;
        }
        st.n = sz(s);
        FER(i, 0, sz(s)) st.t[i + st.n] = mp((int)(s[i] - '0'), i);
        st.build();
       // FER(i, 0, 2 * st.n) cout << st.t[i].ff << " " << st.t[i].ss << endl;
        int pos = 0;
        int falta = k;
        string ans = "";
        while(pos + falta< st.n){
            //cout << pos << " " << falta << " " << st.n << endl;
            ii res = st.query(pos, pos + falta + 1);
            int newpos = res.ss, val = res.ff;
            int quita = newpos - pos;
            falta -= quita;
            //cout << quita << " " << newpos << endl;
            pos = newpos + 1;
            ans += (char)(val + '0');
        }
        cout << ans << endl;
    }
    return 0;
}