单选题 ______ for any reason you are unable to attend tomorrow's meeting, please notify Ms. Clifton as soon as possible so that the catering arrangements can be modified.

A、 Though
B、 If
C、 Except that
D、 Unless

【正确答案】 B

【答案解析】选择符合句意的从属连词。主句是祈使句please notify Ms. Clifton... arrangements can be modified，从句应为条件句。答案是(B)if。