Question

 My father warned me      going to the West Coast because it was crowded with tourists.

A. by      B. on     C. for     D. against

Answer

 D.

考点：考查介词用法。

句意：我父亲警告我不要去西海岸，因为那里挤满了游客。

解析：句中谓语动词warned和介词against搭配，构成warn sb. against doing sth.相当于warn sb. not to do sth， 意思是“警告某人不要干某事”。