_____ Monday morning he wrote an article on grammar. _____ Monday morning he had written an article on grammar.

1. A.
   By
2. B.
   On
3. C.
   At
4. D.
   ／

_____ Monday morning he wrote an article on grammar. 

_____ Monday morning he had written an article on grammar. 

A. By    B. On    C. At      D. ／