#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
typedef long long int lld;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define trav(a,v) for(auto a:v)
vector<pair<int,int> >op;
void solve(){
	op.clear();
	string A,B;
	cin>>A>>B;
	if(A=="1"){
		if(B=="1"){
			cout<<"0\n\n";
			return;
		}
		cout<<"-1\n";
		return;
	}
	if(B=="1"){
		cout<<"1\n";
		return;
	}
	while(A.size()>2 || A[1]=='1'){
		if(A[1]=='1'){
			op.push_back({0,1});
			op.push_back({1,2});
			A="10"+A.substr(2,A.size()-2);
		}else{
			op.push_back({1,2});
			A="1"+A.substr(2,A.size()-2);
		}
	}
	while(A.size()<B.size()){
		op.push_back({0,1});
		op.push_back({0,1});
		A="10"+A.substr(1,A.size()-1);
	}
	rep(i,1,(int)A.size()){
		op.push_back({i-1,i});
		A[i]='1';
	}
	for(int i=A.size()-1;i>0;i--){
		if(A[i]!=B[i]){
			op.push_back({i-1,i});
			op.push_back({i,i+1});
		}
	}
	assert(op.size()<=512);
	cout<<op.size()<<"\n";
	trav(a,op)cout<<a.first+1<<" "<<a.second+1<<"\n";
}

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	int tt=1;
	cin>>tt;
	while(tt--){
		solve();
	}
}