什么是二次富集作用？
参考答案：
就是在浮选过程中进行的那种清洗污染精煤的细矸石颗粒和集中精煤颗粒的作用。
"The risk" mentioned in the text probably refers to ______.
A．a possibility that there will be more climate changes
B．a potential that sea level will possibly keep rising
C．temperature rises that are expected to affect all countries
D．a prediction warning human beings not to ruin the environment
以下哪个部位不是寻常型银屑病的好发部位（）
A.头皮
B.肛门.生殖器
C.肘.膝
D.骶部
E.大关节屈侧
