下列选项中，酸的通性是（）。
A、与活泼金属反应可产生氢气
B、可以与碱反应
C、PH值小于7
D、有腐蚀性
参考答案：A, B, C
The girl with two cats in the yard when the earthquake happened.
A. was playing B. is playing C. are playing D. were playing
影子价格是商品或生产要素的任何边际变化对国家的基本社会经济目标所做贡献的价值，因而，影子价格是（）。
A.市场价格
B.反映市场供求状况和资源稀缺程度的价格
C.计划价格
D.理论价格
. is playing C. are playing D. were playing