#include<iostream> #include<cstring> using namespace std; int main() { string s[20],ans,com; int t,n; cin>>t; while(t--) { ans.clear(); cin>>n; for(int i=0;i<n;i++) cin>>s[i]; for(int i=3;i<=60;i++) for(int j=0;i+j<=60;j++) { com=s[0].substr(j,i); bool flag=true; for(int k=1;k<n;k++) if(s[k].find(com)==string::npos) { flag=0;break; } if(flag&&(com.length()>ans.length()||com.length()==ans.length()&&com<ans)) ans=com; } if(ans.length()) cout<<ans<<endl; else cout<<"no significant commonalities"<<endl; } return 0; } string::find 找到返回起点,否则返回string::npos