Though ________, swimming does us much good．

A.tired

B.we tire out

C.tiring

D.it is tired

答案及解析： C

解析：

分析句子的结构和逻辑关系，此句前后是让步关系。可以把though remember 看成是一个省略句，相当于：Though swimming is tiring，这里swimming与tiring是系表结构，表示属性，所以选tiring。