Look ! The building which now will be used as a library.A. is being builtB. to be builtC.

问题补充：

Look ! The building which now will be used as a library.

A. is being built

B. to be built

C. is built

D. being built

答案：

(答案→)A. is being built

B. to be built

C. is built

D. being built

解析：which now是定语从句，根据now，从句谓语要用现在进行时态，且主语which，即The building，和build是动宾关系，所以用现在进行时态的被动语态。选A。