In the following procedure P, P and B are both procedures; each statement line in and outside the loop counts 1 step.

Procedure P(array1[a1, a2, ..., an])
1. if n<9 exit.
2. call B(array1[a1, a2, ..., an])
   declare new empty array2, array3, array4;
3. for (i=1 to n)
4. { if ((i mod 9)=1)   insert ai into array2;
5.   if ((i mod 9)=4)   insert ai into array3;
6.   if ((i mod 9)=7)   insert ai into array4 }
8. call P( array2 );
9. call P( array3 );
10. call P (array4);

In order to make P's complexity $O(n)$, which of the following can be B's complexity? ($m$ is the input size of B)