The boys don’t know .A. how do they swim B. how swimC. they how swim D. how to swim

问题补充：

The boys don’t know .

A. how do they swim

B. how swim

C. they how swim

D. how to swim

答案：

A. how do they swim

B. how swim

C. they how swim

(答案→)D. how to swim

解析：本题的含义是男孩们不知道如何去游泳，疑问词how+动词不定式to do代替从句，故本题选D。