#include<bits/stdc++.h>
using namespace std;
namespace my_std{
	#define ll long long
	#define bl bool
	ll my_pow(ll a,ll b,ll mod){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res=(res*a)%mod;
			a=(a*a)%mod;
			b>>=1;
		}
		return res;
	}
	ll qpow(ll a,ll b){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res*=a;
			a*=a;
			b>>=1;
		}
		return res;
	}
	#define db double
	#define pf printf
	#define pc putchar
	#define fr(i,x,y) for(register ll i=(x);i<=(y);i++)
	#define pfr(i,x,y) for(register ll i=(x);i>=(y);i--)
	#define go(u) for(ll i=head[u];i;i=e[i].nxt)
	#define enter pc('\n')
	#define space pc(' ')
	#define fir first
	#define sec second
	#define MP make_pair
	#define il inline
	#define inf 1e18
	#define random(x) rand()*rand()%(x)
	#define inv(a,mod) my_pow((a),(mod-2),(mod))
	il ll read(){
		ll sum=0,f=1;
		char ch=0;
		while(!isdigit(ch)){
			if(ch=='-') f=-1;
			ch=getchar();
		}
		while(isdigit(ch)){
			sum=sum*10+(ch^48);
			ch=getchar();
		}
		return sum*f;
	}
	il void write(ll x){
		if(x<0){
			x=-x;
			pc('-');
		}
		if(x>9) write(x/10);
		pc(x%10+'0');
	}
	il void writeln(ll x){
		write(x);
		enter;
	}
	il void writesp(ll x){
		write(x);
		space;
	}
}
using namespace my_std;
vector<pair<ll,ll> > ans;
vector<ll> A,B,S0,S2;
ll t,n,c[1000010];
il void solve1(){
	S0.clear();
	S2.clear();
	fr(i,1,n){
		if(c[i]%4==0) S0.push_back(c[i]);
		else S2.push_back(c[i]);
	}
	while(1){
		if((ll)S0.size()>=2){
			ll x=S0.back(),y;
			S0.pop_back();
			y=S0.back();
			S0.pop_back();
			ans.push_back(MP(x,y));
			if(((x+y)/2)%4==0) S0.push_back((x+y)/2);
			else S2.push_back((x+y)/2);
			continue;
		}
		if((ll)S2.size()>=2){
			ll x=S2.back(),y;
			S2.pop_back();
			y=S2.back();
			S2.pop_back();
			ans.push_back(MP(x,y));
			if(((x+y)/2)%4==0) S0.push_back((x+y)/2);
			else S2.push_back((x+y)/2);
			continue;
		}
		break;
	}
	if(!S0.empty()&&!S2.empty()) ans.push_back(MP(S0[0],S2[0]));
}
il bl chk0(){
	ll d=0;
	fr(i,1,60){
		bl ck=0;
		fr(j,0,(ll)B.size()-1) if(((B[j]>>i)&1)!=((B[0]>>i)&1)) ck=1;
		if(ck){
			d=i;
			break;
		}
	}
	if(!d) return 0;
	ll id=0;
	fr(i,0,(ll)B.size()-1) if((B[i]>>d)&1) id=i;
	swap(B[(ll)B.size()-1],B[id]);
	fr(i,0,(ll)B.size()-1) if(!((B[i]>>d)&1)) id=i;
	swap(B[(ll)B.size()-2],B[id]);
	pfr(i,d-1,1){
		if((ll)B.size()<=2) return 0;
		ll x=B.back(),y;
		B.pop_back();
		y=B.back();
		B.pop_back();
		ans.push_back(MP(x,y));
		B.push_back((x+y)/2);
	}
	return 1;
}
il bl chk1(){
	fr(i,0,(ll)ans.size()-1){
		ans[i].fir++;
		ans[i].sec++;
	}
	swap(A,B);
	fr(i,0,(ll)A.size()-1) A[i]++;
	fr(i,0,(ll)B.size()-1) B[i]++;
	return chk0();
}
il void solve2(){
	ll a=0,b=0;
	fr(i,0,(ll)B.size()-1) if(B[i]%4==0) a=i;
	swap(B[(ll)B.size()-1],B[a]);
	fr(i,0,(ll)B.size()-1) if(B[i]%4==2) b=i;
	swap(B[(ll)B.size()-2],B[b]);
	a=B.back();
	B.pop_back();
	b=B.back();
	B.pop_back();
	while(1){
		if((ll)A.size()>=2){
			ll x=A.back(),y;
			A.pop_back();
			y=A.back();
			A.pop_back();
			ans.push_back(MP(x,y));
			if(((x+y)/2)&1) A.push_back((x+y)/2);
			else B.push_back((x+y)/2);
			continue;
		}
		if((ll)B.size()>=2){
			ll x=B.back(),y;
			B.pop_back();
			y=B.back();
			B.pop_back();
			ans.push_back(MP(x,y));
			if(((x+y)/2)&1) A.push_back((x+y)/2);
			else B.push_back((x+y)/2);
			continue;
		}
		break;
	}
	if(A.empty()){
		if(B[0]%4==0){
			ans.push_back(MP(a,B[0]));
			ans.push_back(MP((a+B[0])/2,b));
		}
		else{
			ans.push_back(MP(b,B[0]));
			ans.push_back(MP((b+B[0])/2,a));
		}
	}
	else if(B.empty()){
		ans.push_back(MP(a,b));
		ans.push_back(MP((a+b)/2,A[0]));
	}
	else{
		if(B[0]%4==0){
			if((a/4+b/4+A[0]/2)&1){
				ans.push_back(MP(a,b));
				ans.push_back(MP((a+b)/2,A[0]));
				ans.push_back(MP(((a+b)/2+A[0])/2,B[0]));
			}
			else if((B[0]/4+b/4+A[0]/2)&1){
				ans.push_back(MP(B[0],b));
				ans.push_back(MP((B[0]+b)/2,A[0]));
				ans.push_back(MP(((B[0]+b)/2+A[0])/2,a));
			}
			else{
				ans.push_back(MP(a,B[0]));
				ans.push_back(MP((a+B[0])/2,b));
				ans.push_back(MP(((a+B[0])/2+b)/2,A[0]));
			}
		}
		else{
			if((a/4+b/4+A[0]/2)&1){
				ans.push_back(MP(a,b));
				ans.push_back(MP((a+b)/2,A[0]));
				ans.push_back(MP(((a+b)/2+A[0])/2,B[0]));
			}
			else if((a/4+B[0]/4+A[0]/2)&1){
				ans.push_back(MP(a,B[0]));
				ans.push_back(MP((a+B[0])/2,A[0]));
				ans.push_back(MP(((a+B[0])/2+A[0])/2,b));
			}
			else{
				ans.push_back(MP(b,B[0]));
				ans.push_back(MP((b+B[0])/2,a));
				ans.push_back(MP(((b+B[0])/2+a)/2,A[0]));
			}
		}
	}
}
il void clr(){
	ans.clear();
	A.clear();
	B.clear();
}
int main(){
	t=read();
	writeln(t);
	while(t--){
		n=read();
		writeln(n);
		fr(i,1,n) c[i]=read();
		fr(i,1,n) writesp(c[i]);
		enter;
		fr(i,1,n){
			if(c[i]&1) A.push_back(c[i]);
			else B.push_back(c[i]);
		}
		if(A.empty()){
			solve1();
			fr(i,0,(ll)ans.size()-1) pf("%lld %lld\n",ans[i].fir,ans[i].sec);
		}
		else if(B.empty()){
			fr(i,1,n) c[i]++;
			solve1();
			fr(i,0,(ll)ans.size()-1) pf("%lld %lld\n",ans[i].fir-1,ans[i].sec-1);
		}
		else if(chk0()){
			solve2();
			fr(i,0,(ll)ans.size()-1) pf("%lld %lld\n",ans[i].fir,ans[i].sec);
		}
		else if(chk1()){
			solve2();
			fr(i,0,(ll)ans.size()-1) pf("%lld %lld\n",ans[i].fir-1,ans[i].sec-1);
		}
		else writeln(-1);
		clr();
	}
}