体积比例浓度计算定义：是指（）与（）之比值。
A.溶质（或浓溶液）体积
B.溶剂体积
C.气体
D.水分
参考答案：A, B
If city noises _____ from increasing, people _____ shout to be heard even at the dinner table
20 years from now. [ ]
A. are not kept; will have to
B. are not kept; have to
C. do not keep; will have to
D. do not keep; have to
以下哪种方式是相对过剩人口的潜在形式（）。
A、农业中的过剩人口
B、结构性失业
C、工作不固定人口
D、等待救济人口
