#include<bits/stdc++.h>
#define INF 2147483647LL
#define int long long
#define MAXN 300005
#define mod 1000000007
#define PI 3.14
#define eps 1e-10
#define pa pair<int,int>
#define ms(a,x) memset(a,x,sizeof(a))
#define mc(ar1,ar2) memcpy(ar1,ar2,sizeof(ar2))
#define mkp(a,b) make_pair(a,b)
#define ls (p<<1)
#define rs (p<<1|1)
#define fn(i,st,ed) for(int i=st;i<=ed;++i)
#define fd(i,st,ed) for(int i=st;i>=ed;--i)
#define fg(i,x,head,e) for(int i=head[x];~i;i=e[i].nxt)
using namespace std;
inline int read(){int x=0,f=1;char c=getchar();while(!isdigit(c)){if(c=='-')f=-1;c=getchar();}while(isdigit(c)){x=x*10+c-'0';c=getchar();}return x*f;}
vector<pa>v;
void solve(){
    string s1,s2;cin>>s1>>s2;
    if((s1=="1")^(s2=="1")){cout<<-1<<endl;return;}
    int n1=s1.size(),n2=s2.size(),ans=0;
    fn(i,1,n1-1)if(s1[i]=='0'){
        ans++;
        v.push_back({i,i+1});
    }
    if(n1<n2)fn(i,n1-1,n2-2){
        ans+=3;
        v.push_back({i,i+1});
        v.push_back({i,i+1});
        v.push_back({i+1,i+2});
    }
    else if(n1>n2){
        fd(i,n2-1,n1-1){
            ans++;
            v.push_back({i-1,i});
        }
        ans+=2;
        v.push_back({n2,n2+(n2-n1+1)*2-1});
        v.push_back({n2-1,n2});
    }
    fd(i,n2-1,0)if(s2[i]=='0'){
        ans+=2;
        v.push_back({i,i+1});
        v.push_back({i+1,i+2});
    }
    cout<<ans<<endl;
    for(auto i:v)cout<<i.first<<' '<<i.second<<endl;
    v.clear();
}
signed main(){
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int T;cin>>T;
    while(T--){solve();}
    return 0;
}