/* SRIJON
        SINGHA
            SAMANTA */
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef long double ld;
#define nl "\n"
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define yes cout << "YES" << nl
#define no cout << "NO" << nl
#define fi first
#define sec second
#define pb push_back
#define ppb pop_back
#define pf push_front
#define ppf pop_front
#define FIO                           \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL);
const int mod = 1e9 + 7;

int32_t main()
{
    FIO

    ll t;	cin>>t;
    ll tt=t;
    while (tt--)
    {
        ll n,k; cin>>n>>k;
        string s;   cin>>s;

        for(ll i=0;i<k;i++)
        {
            char mn='?';
            ll idx;

            for(ll j=0;j<n;j++)
            {
                if(s[j]<mn)
                {
                    mn=s[j];
                    idx=j;
                }           
            }
            s[idx]='?';          
        }
        string x;
        for(ll i=0;i<n;i++) x.pb('?');
        if(s==x)
        {
            cout<<"0"<<nl;
            continue;
        }
        
        for(ll i=0;i<n;i++)
        {
            if(s[i]!='?')   cout<<s[i];           
        }
        cout<<nl;      
    }

    return 0;
}