____ students have graduated from this school in the last twenty years.

1. A.
   Tens of thousands of
2. B.
   Tens upon thousands of
3. C.
   Tens in thousands
4. D.
   Ten thousands of

____ students have graduated from this school in the last twenty years.

A. Tens of thousands of        B. Tens upon thousands of

C. Tens in thousands                    D. Ten thousands of