They learned it all by themselves. That is to say nobody told them .A. what to do itB. ho

问题补充：

They learned it all by themselves. That is to say nobody told them .

A. what to do it

B. how to do it

C. where to do

D. when to do

答案：

A. what to do it

(答案→)B. how to do it

C. where to do

D. when to do

解析：句意：他们是自学的这些技能。也就是说没有人告诉他们该如何去做这些事。本句考查特殊疑问词+to do做宾语；A项中it多余；C和D项少了it；结合句意可知，B项符合要求；故选B。