var
s:array[1..4000] of string;
a:array[1..10] of string;
f:array[1..4000] of string;
k,m,n,c,i:longint;

procedure init;
var  i:longint;
begin
 readln(n);
 for i:=1 to n do
  readln(a[i]);
end;

procedure task1;
var   i,j:longint;
      x,y:string;
begin
 x:=a[1];
 k:=0;
  for i:=1 to length(x) do
   begin
    y:='';
    for j:=i to length(x) do
     begin
      y:=y+x[j];
      if length(y)>=2 then begin inc(k);s[k]:=y; end;
     end;
   end;
end;

procedure  dfs(const x:string;  j:longint);
begin
 if (j=n)and(pos(x,a[j])<>0)then begin inc(c);f[c]:=x;exit;end;
 if pos(x,a[j])=0 then exit
                  else dfs(x,j+1);
end;
procedure sort;
var i,j:longint;
    x,y:string;
     f1:boolean;
begin
 for i:=1 to c  do
  for j:=i+1 to c  do
   if length(f[i])<length(f[j]) then begin
                                      y:=f[i];
                                      f[i]:=f[j];
                                      f[j]:=y;
                                     end;
 for i:=1 to c do
  if length(f[i])<>length(f[i+1]) then begin c:=i;break;end;
 for i:=1 to c do
  begin
   if f[1]>f[i] then f[1]:=f[i];
  end;
 if f[1]='' then writeln('no significant commonalities')
            else writeln(f[1]);
end;

procedure main;
var i:longint;
begin
 c:=0;
 for i:=1 to k do
  begin
   dfs(s[i],2);
  end;
end;

begin
 readln(m);
 for i:=1 to m do
  begin
   init;
   task1;
   main;
   sort;
  end;
end.