#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int MAXN = 1e6 + 5;
const ll linf = 0x3f3f3f3f3f3f3f3f;

#define bbitl(i) (1ll<<(i))
#define bdigl(x,i) ((ll(x)>>(i))&1)
#define lowbit(x) ((x)&-(x))

void solve_sp(vector<ll> a)
{
	vector<ll> vec[2];
	for(auto t: a)
		vec[bdigl(t,1)].emplace_back(t);
	
	auto upd = [&] (int i,int j)
	{
		ll x = vec[i].back(); vec[i].pop_back();
		ll y = vec[j].back(); vec[j].pop_back();
		
		printf("%lld %lld\n",x,y);
		
		ll z = (x + y) / 2;
		vec[bdigl(z, 1)].emplace_back(z);
	};
	
	while(vec[0].size() >= 2 || vec[1].size() >= 2)
	{
		if(vec[0].size() >= 2) upd(0, 0);
		if(vec[1].size() >= 2) upd(1, 1);
	}
	while(vec[0].size() && vec[1].size()) upd(0, 1);
}

vector< pair<ll,ll> > seq;

bool dfs(vector<ll> a)
{
	if(a.size() == 1)
	{
		for(auto t: seq)
			printf("%lld %lld\n",t.first,t.second);
		return 1;
	}
	for(int i=0; i<(int)a.size(); ++i)
		for(int j=0; j<i; ++j) if((a[i] & 1) == (a[j] & 1))
		{
			auto na = a;
			seq.emplace_back(a[i], a[j]);
			na[i] = (a[i] + a[j]) >> 1;
			na.erase(na.begin() + j);
			
			if(dfs(na)) return 1;
			
			seq.pop_back();
		}
	return 0;
}

vector<ll> rt;

void check(vector<ll> &vec)
{
	pair<ll,ll> res = {linf, linf};
	for(auto t: vec) if(t != vec[0])
		res = min(res, make_pair(lowbit(t ^ vec[0]), t));
	
	if(res.first == linf)
		return;
	
	int k = 63 - __builtin_clzll(res.first);
	if((int)vec.size() < k + 1)
		return;
	
	ll x = vec[0], y = res.second;
	vec.erase(vec.begin());
	vec.erase(find(vec.begin(), vec.end(), res.second));
	
	for(int i=1; i<=k-1; ++i)
	{
		printf("%lld %lld\n",x,y);
		x = (x + y) / 2;
		y = vec.back(); vec.pop_back();
	}
	
	rt = {x,y};
}

void solve(void)
{
	int n;
	scanf("%d",&n);
	vector<ll> vec[2];
	for(int i=1; i<=n; ++i)
	{
		ll x;
		scanf("%lld",&x);
		vec[x & 1].emplace_back(x);
	}
	
	if(!vec[0].size()){ solve_sp(vec[1]); return;}
	if(!vec[1].size()){ solve_sp(vec[0]); return;}
	
	rt.clear();
	check(vec[0]);
	if(!rt.size())
		check(vec[1]);
	
	if(!rt.size())
	{
		printf("-1\n");
		return;
	}
	
	auto upd = [&] (int i,int j)
	{
		ll x = vec[i].back(); vec[i].pop_back();
		ll y = vec[j].back(); vec[j].pop_back();
		
		printf("%lld %lld\n",x,y);
		
		ll z = (x + y) / 2;
		vec[bdigl(z, 1)].emplace_back(z);
	};
	
	while(vec[0].size() >= 2 || vec[1].size() >= 2)
	{
		if(vec[0].size() >= 2) upd(0, 0);
		if(vec[1].size() >= 2) upd(1, 1);
	}
	
	if(vec[0].size()) rt.emplace_back(vec[0][0]);
	if(vec[1].size()) rt.emplace_back(vec[1][0]);
	
	seq.clear();
	dfs(rt);
}

int main(void)
{
	int T;
	scanf("%d",&T);
	while(T--) solve();
	return 0;
}