Living in a house on a mountain top _____ be rather cold, especially in winter. [ ]

A. can

B. shall

C. need

D. should

民用建筑内疏散走道、疏散楼梯间、前室室内的装修材料燃烧性能低于（）级的，可以判定为重大火灾隐患。

A.A

B.B1

C.B2

D.B3