#include<bits/stdc++.h>
#define endl '\n'
#define int long long
#define pb push_back
using i64 = long long;
using ll = long long;
using namespace std;
constexpr int N = 2e6 + 10;
string a,b;
vector<pair<int,int>>res;
void fun11to10(int l,int r)
{
    res.pb({l,r});
    res.pb({l+1,l+2});
    string s=a.substr(0,l+1);
    string t;
    if(r+1<a.size())t=a.substr(r+1,a.size());
    a=s+'0'+t;
}
void fun10to11(int l,int r)
{
    res.pb({l,r});
    string s=a.substr(0,l+1);
    string t;
    if(r+1<a.size())t=a.substr(r+1,a.size());
    a=s+'1'+t;
}
void fun11to111(int l,int r)
{
    res.pb({l,r});
    res.pb({l,l+1});
    res.pb({l+1,l+2});
    string s=a.substr(0,r);
    string t=a.substr(r,a.size());
    a=s+'1'+t;
}
void fun01to1(int l,int r)
{
    res.pb({l,r});
    string s=a.substr(0,l);
    string t=a.substr(r,a.size());
    a=s+t;
}
void fun00to0(int l,int r)
{
    res.pb({l,r});
    string s=a.substr(0,l);
    string t;
    if(r+1<a.size())t=a.substr(r+1,a.size());
    a=s+'0'+t;
}
void solve(){
    
    cin>>a>>b;
    a=" "+a;
    b=" "+b;
    //00 -0
    res.clear();
    if(a.size()==2)
    {
        if(b.size()!=2||b[1]!=a[1])cout<<-1<<endl;
        else
        {
            cout<<0<<endl;
        }
        return ;
    }
    if(b.size()==2)
    {
        cout<<-1<<endl;
        return ;
    }
    for(int i=1;i+1<a.size();i++)
    {
        if(a[i]=='1'&&a[i+1]=='0')
        {
            fun10to11(i,i+1);
        }
    }
    //cout<<a<<endl;
    for(int i=a.size()-2;i>=1;i--)
    {
        fun11to10(i,i+1);
    }
    //cout<<a<<endl;
    fun00to0(2,a.size()-1);
    //cout<<a<<endl;
    fun10to11(1,2);
    //cout<<a<<endl;
    while(a.size()<b.size())
    {
        fun11to111(1,2);
    }
    //cout<<a<<endl;
    for(int i=a.size()-2;i>=1;i--)
    {
        if(a[i]=='1'&&a[i+1]=='1'&&b[i]=='1'&&b[i+1]=='0')
        {
            fun11to10(i,i+1);
        }
    }
    cout<<res.size()<<endl;
    for(auto [l,r]:res)
    {
        cout<<l<<" "<<r<<endl;
    }
}

signed main(){
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;
     cin >> t;
    while(t--)solve();
    return 0;
}