Mary dropped in ____ Mr Smith, but he  wasn' t at home, so she went to drop in ____ Mr Smith's office.

1. A.
   on, on
2. B.
   at, at
3. C.
   on. at
4. D.
   at. on

Mary dropped in ____ Mr Smith, but he  wasn' t at home, so she went to drop in ____ Mr Smith's office.          

A. on, on         B. at, at          C. on. at          D. at. on

Mary dropped in ____ Mr Smith, but he  wasn' t at home, so she went to drop in ____ Mr Smith's office.          

A. on, on         B. at, at          C. on. at          D. at. on

Mary dropped in ____ Mr Smith, but he  wasn' t at home, so she went to drop in ____ Mr Smith's office.          

A. on, on         B. at, at          C. on. at          D. at. on

Mary dropped in ____ Mr Smith, but he  wasn' t at home, so she went to drop in ____ Mr Smith's office.          

A. on, on         B. at, at          C. on. at          D. at. on