问题
选择题
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
答案
答案：C
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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
答案：C