B

#include <bits/stdc++.h>
using namespace std;

#define ll     long long
#define _test   int _TEST; cin>>_TEST; while(_TEST--)
#define pb     push_back

int main()
{
    _test
    {
        int n, k;
        cin>>n>>k;

        string s;
        cin>>s;

        if(k%2 == 0)
        {
            sort(s.begin(), s.end());
            cout<<s<<"\n";
            continue;
        }

        vector<char> v;
        for(int i=0; i<n; i+=2)
            v.pb(s[i]);

        sort(v.begin(), v.end());

        for(int i=0, j=0; i<n; i+=2)
            s[i] = v[j++];

        v.clear();
        for(int i=1; i<n; i+=2)
            v.pb(s[i]);

        sort(v.begin(), v.end());

        for(int i=1, j=0; i<n; i+=2)
            s[i] = v[j++];

        cout<<s<<"\n";
    }
}