#include<cstdio>

 #include<queue>

 #include<vector>

 #include<cstring>

 #define FOR(a,b,c) for(int a=(b);a<=(c);a++)

 using namespace std;

 const int maxn = +;

 const int N=;

 struct Node{

     int u,v;

 };

 int n,m;

 int deg[maxn],G[maxn][maxn];

 vector<Node> ans;

 void euler(int u) {

     FOR(v,,N) if(G[u][v]) {

               G[u][v]--; G[v][u]--;

               euler(v);

               ans.push_back((Node){u,v});

        }

 }

 int main() {

     int T,kase=;

     scanf("%d",&T);

     while(T--)

     {

         memset(deg,,sizeof(deg));

         memset(G,,sizeof(G));

         scanf("%d",&n);

         int u,v,start=-;

         FOR(i,,n) {

             scanf("%d%d",&u,&v);

             G[u][v]++; G[v][u]++;

             deg[u]++; deg[v]++;

             start=u;

         }

         bool solved=true;

         FOR(i,,N)  if(deg[i]&) { solved=false; break; }

         if(solved) {

             ans.clear();

             euler(start);

             if(ans.size()!=n || ans[].v!=ans[ans.size()-].u) solved=false;  //注意ans是逆序

         }

         printf("Case #%d\n",++kase);

         if(!solved) printf("some beads may be lost\n");

         else

            for(int i=ans.size()-;i>=;i--) printf("%d %d\n",ans[i].u,ans[i].v);

         if(T) putchar('\n');

     }

     return ;

 }