《2016年中国水资源公报》数据显示：河流水质2016年，对全国23.5万km的河流水质状况进行了评价，Ⅰ～Ⅲ类水河长占76.9%，劣V类水河长占9.8%，主要污染项目是氨氮、总磷、化学需氧量。与2015年同比，Ⅰ～Ⅲ类水河长比例上升3.5个百分点，劣Ⅴ类水河长比例下降1.7个百分点。从以上可以推断我国河流目前的主要污染物来源为
A. 化肥
B. 重金属
C. 耗氧有机污染物
D. 放射性物质
查看答案
POPs持久性有机污染物容易
A. 致癌
B. 致突变
C. 致畸
D. 致水体富营养化
A price taker is
A. a firm that accepts different prices from different customers.
B. a consumer who accepts different prices from different firms.
C. a perfectly competitive firm.
D. a firm that cannot influence the market price.
E. both C and D
Which of following is a key assumption of a perfectly competitive market?
A. Firms can influence market price.
B. Commodities have few sellers.
C. It is difficult for new sellers to enter the market.
D. Each seller has a very small share of the market.
E. none of the above
A few sellers may behave as if they operate in a perfectly competitive market if the market demand is:
A. highly inelastic.
B. very elastic.
C. unitary elastic.
D. composed of many small buyers.
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