In the library I found a useful book how to use English grammar.A. to explainB. explaine

问题补充：

In the library, I found a useful book how to use English grammar.

A. to explain

B. explained

C. having explained

D. explaining

答案：

A. to explain

B. explained

C. having explained

(答案→)D. explaining

解析：考查现在分词做定语，因为book和explain是主动关系，用现在分词做定语，句意是：在图书馆，我发现一本有用的解释怎么使用英语语法的书。选D。