一般说来，战时留城人口约占城市总人口的( )。
A．50%B．40%～50%C．30%～40%D．20%～30%
参考答案：C
Hong Kong _______ to be a good place for eating today. [ ]
A. knows
B. knew
C. is known
D. was known
食品在烟熏、烧烤等制作过程中可产生（）
A.热解产物污染
B.苯并芘的污染
C.亚硝胺的污染
D.铅、砷等有害金属污染
E.微生物、病毒等生物性污染
