#ifndef LOCAL
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#endif

#include <bits/stdc++.h>
using namespace std;

using ll=long long;
using uint=unsigned;

#define rng(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,b) rng(i,0,b)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(),x.end()
#define si(x) int(x.size())
#define a first
#define b second
template<class t>using vc=vector<t>;
template<class t,class u>bool chmax(t&a, u b){ if(a<b){a=b;return 1;}return 0;}
template<class t,class u>bool chmin(t&a,u b){if(a>b){a=b;return 1;}return 0;}

using P=pair<int,int>;
template<class t,class u>
ostream& operator<<(ostream& os, const pair<t,u>&p){
	return os<<"{"<<p.a<<","<<p.b<<"}";
}
template<class t> ostream& operator<<(ostream& os,const vc<t>&v){
	os<<"{";
	for(auto e:v)os<<e<<",";
	return os<<"}";
}

void solve(){
	string s,t;cin>>s>>t;
	if(s == t){
		cout<<0<<endl; return;
	}
	if(s == "1" or t == "1"){
		cout<<-1<<endl; return;
	}
	vc<P>ans;
	while(1){
		rep(i,si(s)){
			if(s[i] == '0'){
				rng(j,i+1,si(s)){
					if(s[j] == '1'){
						ans.eb(i, j);
						string ss = s.substr(0,i)+s.substr(j);
						s = ss; //cout<<s<<endl;
						goto nxt;
					}
				}
				//all zero
				rng(j,i-1,si(s)-1){
					//10->11
					ans.eb(j,j+1);
					s[j+1]='1';
					goto nxt2;
				}
			}
		}break;
		nxt:;
	}
	nxt2:;
	//cout<<ans<<endl;
	while(si(s) > 2){
		ans.eb(0,1);
		ans.eb(1,3);
		s.pop_back();
	}
	//s = 11
	int md;
	int m = si(t);
	int len;
	if(t[m-1] == '0') md = 0;
	else{
		for(int i=m-1;i>=-1;i--){
			if(i == -1 or t[i] == '0'){
				if(i == m-2){
					md = 1;
				}
				else{
					md = 2;
					len = (m-2-i);
				
					rng(j,i+2,m) t[j] = '0';
				}
				break;
			}
		}
	}
	//cout<<t<<endl;
	vc<int>L;
	char c;
	int cur;
	rep(i,m){
		if(!i) c=t[i],cur=1;
		else if(c==t[i]) cur++;
		else{
			L.pb(cur);
			c=t[i],cur=1;
		}
	}
	L.pb(cur);
	//cout<<L<<" "<<t<<" "<<md<<endl;
	if(si(L)%2 == 1){
		assert(md == 1);
		L.pop_back();
	}
	//cout << L << endl;
	//11->(10)*si(L)/2
	if(si(L) == 2){
		ans.eb(0,1);
		ans.eb(1,2);
	}
	else{
		ans.eb(0,1); ans.eb(0,1); ans.eb(1,2); ans.eb(0,1);
		ans.eb(1,2); ans.eb(0,2);
		//1010
		for(int i=2;i<si(L)/2;i++){
			ans.eb(0,1); ans.eb(0,1); ans.eb(0,1); ans.eb(1,2); ans.eb(0,1);
			ans.eb(1,2); ans.eb(0,2);
		}
	}
	
	//cout<<ans<<endl;
	//cout<<L<<" "<<md<<endl;
	//{1,..,1}
	int pre = 0;
	rep(i,si(L)){
		if(i%2 == 0){
			rep(j,L[i]-1){
				ans.eb(pre,pre+1);
				ans.eb(pre,pre+1);
				ans.eb(pre,pre+1);
				pre++;
			}
		}
		else{
			if(i+1 == si(L) and md == 1){
				ans.eb(pre,pre+1); ans.eb(pre,pre+1); ans.eb(pre,pre+1);
				ans.eb(pre+1,pre+2); ans.eb(pre,pre+1);
				ans.eb(pre+1,pre+2);
			}
			rep(j,L[i]-1){
				ans.eb(pre,pre+1);
				ans.eb(pre,pre+1);
			}
			if(i+1 == si(L) and md == 2){
				rep(j,len){
					ans.eb(pre,pre+1);
					pre++;
				}
			}
			pre += L[i]+1;
		}
	}
	cout << si(ans) << endl;
	for(auto [x,y]:ans) cout<<x+1<<" "<<y+1<<endl;
}
signed main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	cout<<fixed<<setprecision(20);
	int t;cin>>t;
	while(t--) solve();
}