#include<bits/stdc++.h>
#define mk make_pair
using namespace std;
const int N=500;
vector<pair<int,int> > ans;
void change1(int l) {//  11 -> 111
    pair<int,int> t;
    t.first=l; t.second=l+1; ans.push_back(t);
    t.first=l; t.second=l+1; ans.push_back(t);
    t.first=l+1; t.second=l+2; ans.push_back(t);
}

void change2(int l) {//11 -> 110
    pair<int,int> t;
    t.first=l; t.second=l+1; ans.push_back(t);
    t.first=l; t.second=l+1; ans.push_back(t);
}

void change3(int l) {// 111 -> 11
    pair<int,int> t;
    t.first=l; t.second=l+1; ans.push_back(t);
    t.first=l+1; t.second=l+3; ans.push_back(t);
}

void change4(int l,int sm) {//11 -> 1 0(sm) 1
    if(sm==0) return;
    pair<int,int> t;
    t.first=l; t.second=l+1; ans.push_back(t);
    t.first=l; t.second=l+2; ans.push_back(t);
    t.first=l+1; t.second=l+2; ans.push_back(t);
    for(int i=2;i<=sm;i++) {
        t.first=l; t.second=l+1;  ans.push_back(t);
        t.first=1; t.second=l+1; ans.push_back(t);
    }
}

char s[N],t[N];
int n,m;
bool cmd(char *a,char *b) {
    if(n!=m) return 1;
    for(int i=1;i<=n;i++)
        if(a[i]!=b[i]) return 1;
    return 0;
}
void solve() {
    scanf("%s%s",s+1,t+1); int sum=0;
    n=strlen(s+1); m=strlen(t+1);
    if(cmd(s+1,t+1)==0) {cout<<"0\n"; return;}
    if(n==1 || m==1) {cout<<"-1\n"; return;}
    for(int i=n,lst=0;i>=1;i--) {
        while(s[i]=='0') i--;
        if(!lst) {
            if(i==n) { sum+=1; lst=n; continue;}
            if(i!=n-1) {
                pair<int,int> t;
                t.first=i+1; t.second=n; ans.push_back(t);
            }
            pair<int,int> t; t.first=i; t.second=i+1;
            ans.push_back(t); sum+=2; lst=i;
        } else {
            pair<int,int> t;
            t.first=i+1; t.second=lst; ans.push_back(t);
            if(i+1==lst) ans.pop_back();
            lst=i; sum++;
        }
    }

    for(int i=3;i<=sum;i++) change3(1);

    int ed=2; while(ed<=m && t[ed]=='0') ed++;
    if(ed==m+1) {
        for(int i=3;i<=m;i++) {
            pair<int,int> t;
            t.first=1,t.second=2; ans.push_back(t);
            t.first=1,t.second=2; ans.push_back(t);
        }
        pair<int,int> t;
        t.first=1,t.second=2; ans.push_back(t);
        t.first=2,t.second=3; ans.push_back(t);

        cout<<ans.size()<<"\n";
        for(auto it:ans) cout<<it.first<<" "<<it.second<<"\n";
        return;
    }
    for(int i=m;i>ed;i--) {
        if(t[i]=='0') change2(1);
        else change1(1);
    }
    change4(1,ed-2);
    cout<<ans.size()<<"\n";
    for(auto it:ans) cout<<it.first<<" "<<it.second<<"\n";
}

void init() {
    ans.clear();
}

int main() {
    int T;scanf("%d",&T);
    while(T--) {
        init(); solve();
    }
    return 0;
}

/*
10000
1001
*/