某城市实行阶梯水价，标准范围内每吨水3元，超标准部分每吨5元。某居民某月用水21吨，

下列属于“丝绸之路”上保留至今的文明遗迹是（）。

A．云冈石窟

B．龙门石窟

C．莫高窟

D．大足石刻

5除215和215除5，写出的算式是一样的．______（判断对错）

The foreign friends you referred to________looking forward to________around the university. [      ]

A. being; being shown  

B. are; being shown

C. being; showing  

D. are; be shown

---- I called you 10:30 p.m, but you didn’t answer it.  

----I _____my work and ______a bath.[ ]

A. was doing; had taken        

B. had done; had taken

C. was doing; was taken        

D. had done; was taking

关于苯甲酸与苯甲酸钠防腐剂叙述不正确的是

A．相同浓度的苯甲酸与苯甲酸钠盐其抑菌作用相同

B．在酸性条件下抑菌效果较好，最佳pH值为4

C．pH增高苯甲酸解离度增大抑菌活性下降

D．分子态的苯甲酸抑菌作用强

E．苯甲酸与尼泊金类防腐剂合用具有防霉与防发酵作用