B

#include <bits/stdc++.h>

using namespace std;

#define _test   int _TEST; cin>>_TEST; while(_TEST--)

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

        vector<int> a(2*n);
        for(auto &e: a)     cin>>e;

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

        cout<<a[n-1]-a[0] + a[2*n-1]-a[n]<<"\n";
        for(int i=0; i<n; i++)
            cout<<a[i]<<" "<<a[i+n]<<"\n";
    }
}