Those overseas students volunteer 10 hours each week in Paris free food and accommodation

Those overseas students volunteer 10 hours each week in Paris free food and accommodation.
A. in search of
B. in contact with
C. in case of
D. in exchange for

A. in search ofB. in contact withC. in case of(答案→)D. in exchange for解析：in exchange for与……交换；in search of寻找；in contact with与……接触；in case of在……情形下。句意为：为了换取免费的食宿，那些在巴黎的留学生们每周义务劳动10个小时。故正确答案为D项。

我明天再问问老师，叫他解释下这个问题