#include <bits/stdc++.h>
using namespace std;
#define cs const
#define re register
#define pb push_back
#define y0 sxxxxx
#define pii pair<int, int>
#define ll long long
#define fi first
#define se second
#define bg begin
namespace IO{

cs int RLEN=1<<22|1;
char ibuf[RLEN],*ib,*ob;
inline char gc(){
    (ib==ob)&&(ob=(ib=ibuf)+fread(ibuf,1,RLEN,stdin));
    return (ib==ob)?EOF:*ib++;
}
inline int read(){
    char ch=gc();
    int res=0;bool f=1;
    while(!isdigit(ch))f^=ch=='-',ch=gc();
    while(isdigit(ch))res=(res*10)+(ch^48),ch=gc();
    return f?res:-res;
}
inline ll readll(){
    char ch=gc();
    ll res=0;bool f=1;
    while(!isdigit(ch))f^=ch=='-',ch=gc();
    while(isdigit(ch))res=(res*10)+(ch^48),ch=gc();
    return f?res:-res;
}
inline char readchar(){
	char ch=gc();
	while(isspace(ch))ch=gc();
	return ch;
}
inline int readstring(char *s){
	int top=0;char ch=gc();
	while(isspace(ch))ch=gc();
	while(!isspace(ch)&&ch!=EOF)s[++top]=ch,ch=gc();
	s[top+1]='\0';return top;
}

}
using IO::read;
using IO::readll;
using IO::readchar;
using IO::readstring;
template <typename tp>
inline void chemx(tp &a, tp b) { (a < b) ? (a = b) : 0; }
template <typename tp>
inline void chemn(tp &a, tp b) { (a > b) ? (a = b) : 0; }


cs int N=200005;

int n;
char s[2][N];

#define poly vector<int>


void Add(poly &a,poly b){
    if(a.size()<b.size())a.resize(b.size());
    for(int i=0;i<b.size();i++){
        a[i]+=b[i];
        if(a[i]>9){
            if(i+1==a.size())a.pb(0);
            a[i+1]+=a[i]/10,a[i]%=10;
        }
    }
    int p=b.size();
    while(p<a.size()&&a[p]>9){
        if(p+1==a.size())a.pb(0);
        a[p+1]+=a[p]/10,a[p]%=10,p++;
    }
    
}
bool comp(poly a,poly b){// a<b
    if(a.size()<b.size())return 1;
    if(a.size()>b.size())return 0;
    for(int i=(int)a.size()-1;~i;i--){
        if(a[i]!=b[i]){
            return a[i]<b[i];
        }
    }
    return 0;
}
int lx,rx,ly,ry;
int tmp[N];
poly calc(int l,int r){
    for(int i=1;i<=2*n;i++)tmp[i]=0;
    for(int i=1;i<=n;i++){
        if((i>l&&i<=r)||(i<=l&&i>r)){
            int ps=2*i-1+(i>l);
            if(s[1][ps]!='1')tmp[ps]=1;
            else tmp[ps]=0;
            ps=2*i-1+(i>r);
            if(s[1][ps]!='2')tmp[ps]=2;
            else tmp[ps]=0;            
        }
        else{
            int ps=2*i-1+(i>l);
        //    cout<<i<<" "<<ps<<'\n';
            if(s[0][ps]=='1'||s[1][ps]=='2'){
                tmp[ps]=1;
            }
            else tmp[ps]=2;
        }
    }
  //  cout<<l<<" "<<r<<'\n';
  // for(int i=1;i<=2*n;i++)cout<<tmp[i];puts("");
    poly res(1,0);
    poly now;
    for(int i=1;i<=2*n;i++){
        if(tmp[i]==0){
            if(now.size()){
                reverse(now.begin(),now.end());
                Add(res,now);
                now.clear();
            }
        }
        else{
            now.pb(tmp[i]);
        }
    }
    if(now.size()){
        reverse(now.begin(),now.end());
        Add(res,now);
        now.clear();
    }    
    return res;
}
char ss[2][N];
void get_ans(int l,int r){
  //  cout<<l<<" "<<r<<'\n';
    for(int j=0;j<2;j++){
        for(int i=1;i<=2*n;i++)ss[j][i]='0';
        ss[j][2*n+1]='\0';
    }
    for(int i=1;i<=n;i++){
        if((i>l&&i<=r)||(i<=l&&i>r)){
            int ps=2*i-1+(i>l);
            if(s[1][ps]!='1')ss[0][ps]='1',ss[1][ps]='0';
            else ss[0][ps]='0',ss[1][ps]='1';
            ps=2*i-1+(i>r);
            if(s[1][ps]!='2')ss[0][ps]='2',ss[1][ps]='0';
            else ss[0][ps]='0',ss[1][ps]='2';          
        }
        else{
            int ps=2*i-1+(i>l);
            if(s[0][ps]=='1'||s[1][ps]=='2'){
                ss[0][ps]='1';
                ss[1][ps]='2';

            }
            else ss[0][ps]='2',ss[1][ps]='1';
        }
    }    
    for(int i=0;i<2;i++)cout<<(ss[i]+1)<<'\n';
}
void write(poly x){
    for(int i=(int)x.size()-1;~i;i--)cout<<x[i];
    puts("");
}
void solve(){
    n=read();
    readstring(s[0]);
    readstring(s[1]);
    lx=ly=-1;
    rx=ry=n+1;
    for(int i=n;i;i--){
        int cnt1=0,cnt2=0;
        for(int j=0;j<2;j++)
        for(int k=0;k<2;k++){
            if(s[j][i*2-1+k]=='1'){
                cnt1++;
                if(k==0)lx=max(lx,i);
                else rx=min(rx,i);
            }
            if(s[j][i*2-1+k]=='2'){
                cnt2++;
                if(k==0)ly=max(ly,i);
                else ry=min(ry,i);
            }
        }
        if(cnt1>1||cnt2>1){puts("impossible");return;}
    }
  //  cout<<lx<<" "<<ly<<" "<<rx<<" "<<ry<<'\n';
    for(int i=1;i<=2*n;i++)
    for(int j=0;j<2;j++)if(s[j][i]!='?'){
        if(i>1){
            for(int k=0;k<2;k++)if(s[k][i-1]==s[j][i]){
                puts("impossible");return;
            }
        }
        if(i<2*n){
            for(int k=0;k<2;k++)if(s[k][i+1]==s[j][i]){
                puts("impossible");return;
            }            
        }
    }
    if(lx>rx||ly>ry){
        puts("impossible");return;
    }
    poly f1=calc(lx,ry-1);
    poly f2=calc(rx-1,ly);
    if(comp(f1,f2)){
        write(f2);
        get_ans(rx-1,ly);
    }
    else{
        write(f1);
        get_ans(lx,ry-1);
    }
}

int main() {
	#ifdef Stargazer
	freopen("1.in","r",stdin);
//	freopen("1.out","w",stdout);
	#endif
	int T=read();
    while(T--){
        solve();
    }
}