The mayor is strongly opposed to a new hall which may cost a lot of money. A. buildingB.

问题补充：

The mayor is strongly opposed to a new hall, which may cost a lot of money.

A. building

B. build

C. be building

D. have built

答案：

(答案→)A. building

B. build

C. be building

D. have built

解析：考查动名词用法。固定词组be opposed to sth/doing sth反对sth/做某事；其中的to是介词，后面要接名词或者动名词的形式。句意：市长强烈反对建设一个新的购物中心，那要花去很多的钱。故A正确。