#include<bits/stdc++.h>
#define FileIO freopen("input.in", "r", stdin); freopen("output.in", "w", stdout)
#define ll long long
#define input_vec(v) for(int II=0; II<v.size(); II++) cin >> v[II];
#define sortf(v) sort(v.begin(), v.end());
#define sortr(v) sort(v.rbegin(), v.rend());
#define print_vec(v) for(int II=0; II<v.size(); II++){cout << v[II];} cout << endl;
using namespace std;
void test_case(int tc)
{
int n, k;
cin>>n>>k;
string s;
cin>>s;
int len=s.size();
if(n==k){
cout<<0<<endl;
return;
}
while(k){
int minidx=0;
while(minidx<len && s[minidx]=='*') minidx++;
for(int i=0;i<len;i++){
if(s[i]!='*' && s[i]<s[minidx]){
minidx=i;
}
}
// cout<<"minindex: "<<minidx<<endl;
//remove min index
s[minidx]='*';
k--;
}
for(int i=0;i<len;i++){
if(s[i]!='*') cout<<s[i];
}cout<<endl;
}
int main()
{
//if(fopen("input.in", "r")) FileIO;
int n; cin >> n;
for(int i=0; i<n; i++) test_case(i+1);
}