#include <bits/stdc++.h>
#define ll long long
using namespace std;
int T,n;
vector<ll> v[2];
bool check(vector<ll> S)
{
	if(S.empty())return 1;
	if(S.size()>60)
	{
		for(int i=1;i<S.size();++i)if(S[i]!=S[1])return 1;
		return 0;
	}
	else
	{
		ll x=1ll<<S.size();
		for(int i=1;i<S.size();++i)if((S[i]&x-1)!=(S[0]&x-1))return 1;
		return 0;
	}
}
#define s1 first
#define s2 second
map<ll,vector<ll>> mp;
void shrink(int k)
{
	static vector<ll> del;
	while(!mp.empty())
	{
		auto it=--mp.end();
		if(it->s1<1ll<<k)break;
		auto tt=*it;
		mp.erase(it);
		for(ll x:tt.s2)mp[tt.s1&(1ll<<k)-1].push_back(x);
	}
	del.clear();
	for(auto x:mp)if(x.s2.empty())del.push_back(x.s1);
	for(ll x:del)mp.erase(x);
}
vector<ll> v4[2];
void solve4(vector<ll> &v)
{
	// printf(">>>>>>>>>>>>>>>>solve4(");for(ll x:v)printf("%lld ",x);printf(")\n");
	v4[0].clear();v4[1].clear();
	for(ll &x:v)v4[x>>1&1].push_back(x);
	while(v4[0].size()>=2||v4[1].size()>=2)
	{
		ll x,y;
		if(v4[0].size()>=2)
		{
			x=v4[0].back();v4[0].pop_back();
			y=v4[0].back();v4[0].pop_back();
		}
		else
		{
			x=v4[1].back();v4[1].pop_back();
			y=v4[1].back();v4[1].pop_back();
		}
		ll z=(x+y)/2;
		printf("%lld %lld\n",x,y);
		v4[z>>1&1].push_back(z);
	}
	v.clear();
	for(ll x:v4[0])v.push_back(x);
	for(ll x:v4[1])v.push_back(x);
	// printf("finished solve4\n");
}
int main()
{
	scanf("%d",&T);while(T--)
	{
		scanf("%d",&n);
		v[0].clear();v[1].clear();
		for(int i=1;i<=n;++i){ll x;scanf("%lld",&x);v[x&1].push_back(x);}
		if(n==1)continue;
		bool ok[2]={check(v[0]),check(v[1])};
		if(!ok[0]&&!ok[1])
		{
			printf("-1\n");continue;
		}
		int o=0;
		if(!ok[0])o=1;
		// printf("o:%d\n",o);
		// printf("v[%d]:",0);for(ll x:v[0])printf("%lld ",x);putchar(10);
		// printf("v[%d]:",1);for(ll x:v[1])printf("%lld ",x);putchar(10);
		solve4(v[o^1]);
		if(v[o^1].size()==2)
		{
			printf("%lld %lld\n",v[o^1][0],v[o^1][1]);
			v[o].push_back(v[o^1][0]+v[o^1][1]>>1);
			v[o^1].clear();
		}
		if(v[o^1].empty())
		{
			solve4(v[o]);
			if(v[o].size()==2)printf("%lld %lld\n",v[o][0],v[o][1]);
			continue;
		}
		int tt=v[o].size();
		sort(v[o].begin(),v[o].end());
		while(tt>60)
		{
			--tt;
			ll c[4]={v[o].end()[-4],v[o].end()[-3],v[o].end()[-2],v[o].end()[-1]};
			v[o].pop_back();v[o].pop_back();v[o].pop_back();v[o].pop_back();
			int I=-1,J=-1;
			for(int i=0;i<3;++i)if(c[i]==c[i+1]){I=i;J=i+1;break;}
			if(!~I)
			{
				for(int i=0;i<4;++i)for(int j=i+1;j<4;++j)if((c[i]+c[j])%4==(o<<1))I=i,J=j;
			}
			for(int _=0;_<4;++_)if(_!=I&&_!=J)v[o].push_back(c[_]);
			printf("%lld %lld\n",c[I],c[J]);
			v[o].push_back(c[I]+c[J]>>1);
			sort(v[o].end()-3,v[o].end());
		}
		// printf("after first round v[o]:");for(ll x:v[o])printf("%lld ",x);putchar(10);
		mp.clear();
		for(ll x:v[o])mp[x&(1ll<<tt)-1].push_back(x);
		while(1)
		{
			static vector<pair<ll,int>> vv;
			vv.clear();
			auto it=mp.begin();
			for(int _=0;_<min((int)mp.size(),5);++_)
			{
				vv.push_back({it->s1,it->s2.size()});
				++it;
			}
			// printf("vv:");for(auto x:vv)printf("{%lld,%d} ",x.s1,x.s2);putchar(10);
			int I=-1,J=-1;
			for(int i=0;i<vv.size();++i)
			{
				for(int j=i;j<vv.size();++j)if((vv[i].s1+vv[j].s1)%4==(o<<1))
				{
					if(i==j&&vv[i].s2<2)continue;
					static vector<ll> vt;
					vt.clear();
					for(int _=0;_<vv.size();++_)if(vv[_].s2-(_==i)-(_==j))vt.push_back(vv[_].s1);
					vt.push_back((vv[i].s1+vv[j].s1)/2);
					for(ll &x:vt)x&=(1ll<<tt-1)-1;
					sort(vt.begin(),vt.end());
					int m=unique(vt.begin(),vt.end())-vt.begin();
					if(m>1){I=i;J=j;break;}
				}
				if(~I)break;
			}
			if(!~I)break;
			auto itI=mp.find(vv[I].s1),itJ=mp.find(vv[J].s1);
			ll xI=itI->s2.back();itI->s2.pop_back();
			ll xJ=itJ->s2.back();itJ->s2.pop_back();
			printf("%lld %lld\n",xI,xJ);
			mp[xI+xJ>>1&(1ll<<tt)-1].push_back(xI+xJ>>1);
			shrink(--tt);
		}
		v[o].clear();
		for(auto x:mp)for(ll y:x.s2)v[o].push_back(y);
		// printf("after second part v[o]:");for(ll x:v[o])printf("%lld ",x);putchar(10);
		if(v[o].size()==2)
		{
			printf("%lld %lld\n",v[o][0],v[o][1]);
			ll z=(v[o][0]+v[o][1])/2;
			printf("%lld %lld\n",v[o^1][0],z);
			continue;
		}
		if(v[o].empty())continue;
		mp.clear();
		int I=-1,J=-1;
		for(int i=0;i<v[o].size();++i)
		{
			for(int j=i+1;j<v[o].size();++j)
			{
				// printf("x:%lld y:%lld z:%lld\n",v[o][i],v[o][j],(v[o][i]+v[o][j])/2);
				if((v[o][i]+v[o][j])/2%2==(o^1)&&((v[o][i]+v[o][j])/2+v[o^1][0])/2%2==o){I=i,J=j;break;}
			}
			if(~I)break;
		}
		// printf("I:%d J:%d\n",I,J);
		ll x=v[o][I],y=v[o][J];
		v[o].erase(v[o].begin()+J);
		v[o].erase(v[o].begin()+I);
		printf("%lld %lld\n",x,y);
		printf("%lld %lld\n",(x+y)/2,v[o^1][0]);
		v[o].push_back(((x+y)/2+v[o^1][0])/2);
		solve4(v[o]);
		if(v[o].size()==2)printf("%lld %lld\n",v[o][0],v[o][1]);
	}
	fclose(stdin);fclose(stdout);return 0;
}