#include<bits/stdc++.h>
#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
using namespace std;
typedef double db;
typedef long long ll;
typedef pair<ll,ll> pii;
typedef vector<pii> vii;
typedef vector<ll> vi;
typedef vector<string> vs;
typedef vector<char> vc;
const ll inf=1e18;
const int N=5e5+10;
int n,m,a[N],ls[N];
string s,t;
vii g;
//10->11
//11->100
//00->0
//100->10
void init(int &n,string &s,string &now) {
	s=now; n=s.size(); now="";
}
void upd(int l,int r,int op) {
	if(op==0) g.push_back({l,r});
	else {
		g.push_back({r-1,r});
		g.push_back({r,r+1});
		while(l<r-1) {
			g.push_back({r-2,r-1});
			g.push_back({r-1,r+1});
			r--;
		}
	}
}
void get_10() {
	string as;
	for(int i=1;i<=n;i++) {
		if(s[i-1]=='1') as+='1';
		else {
			int j=i;
			while(j<=n&&s[i-1]==s[j-1]) j++;
			int cnt=j-i+1;
			if(j>n) {
				g.push_back({as.size()+1,as.size()+cnt-1});
				as+='0';
			}
			else {
				g.push_back({as.size()+1,as.size()+cnt});
				as+='1';
			}
			i=j;
		}
	}
	init(n,s,as);//s->1...1 or 1...10
	if(s=="10") return;
	if(s.back()=='1') upd(1,n,1);
	else upd(1,n-1,1),upd(2,3,0);
}
void add0(int l,int r) {//10->100
	g.push_back({l,r});
	g.push_back({l,r});
}
void add(int l,int r,int op,int now) {//10->010 or 110
	if(op==1) {
		g.push_back({l,r});
		g.push_back({l,r});
		g.push_back({l,r});
	}
	else if(a[now-1]=='1') {
		g.push_back({l,r});
		g.push_back({l,r});
		g.push_back({l,r});
		r=l; l=l-1;
		g.push_back({r-1,r});
		g.push_back({r,r+1});
	}
	else {
		int lf=ls[now];
		g.push_back({lf,lf+1});
		g.push_back({lf,lf+1});
	}
}
int main() {
	IOS
	int T;
	cin>>T;
	while(T--) {
		cin>>s>>t;
		n=s.size();
		m=t.size();
		if(s==t) {
			cout<<0<<'\n';
			continue;
		}
		else if(s.size()==1) {
			cout<<-1<<'\n';
			continue;
		}
		else if(t.size()==1) {
			cout<<-1<<'\n';
			continue;
		} 
		else {
			g.clear();
			get_10();
			s="10"; n=2;
			for(int i=1;i<=m;i++) {
				if(t[i-1]=='1') ls[i]=i;
				else ls[i]=ls[i-1];
				a[i]=t[i-1]-'0';
			}
			for(int i=1;i<=m;i++) {
				if(t[i-1]=='1') add(n-1,n,1,i);
				else add(n-1,n,0,i);
				n++;
			}
			if(a[m]+a[m-1]==2) {
				upd(n-3,n-1,1); n--;
				upd(n-1,n,0); n--;
				g.push_back({m-1,m});
			}
			else if(a[m]+a[m-1]==0) {
				int lf=ls[m];
				g.push_back({lf+1,n-1}); n-=(m-lf);//10...010->110
				upd(lf,lf+1,1);//110->100
				while(n<m) add0(lf,lf+1),n++;//100->10...0
			}
			else if(a[m]==1) {//110
				g.push_back({n-1,n});//110->111
				upd(n-2,n,1); n--; //111->10
				g.push_back({n-1,n});//10->11
				int lf=ls[m-1];
				g.push_back({lf+1,m}); n-=(m-lf-1); //1...011->111
				upd(lf,lf+1,1);//111->101
				while(n<m) add0(lf,lf+1),n++;//101->10...01
			}
			else if(a[m-1]==1) {
				g.push_back({n-3,n-2});
				upd(n-3,n-1,1); n--;
				upd(n-1,n,0); n--;
			}
			cout<<g.size()<<'\n';
			for(auto v:g) cout<<v.first<<' '<<v.second<<'\n';
		}
	}
    return 0;
}