The construction of the laboratory _B___by the end of next month.
A) must be completed
B) must have been completed
C) will be completing
D) will have been completing
----"by end of +将来时间",动词用“将来完成时”,又由于The construction of the laboratory(实验室的建设)不会自己完成,应用被动语态,所以排除D,只能选完成时被动语态的B.