单项式-2x3y2z5的系数是______；若am-2bn+7与-3a4b4是同

桥式起重机大车滑线端的端梁下应设置（）以防止（）与（）相接触。

焦炭偏生导致机械强度（）。

A、降低

B、无影响

C、增加

主要用于反映肝细胞损伤的酶是（）

A.脯氨酰羟化酶

B.单胺氧化酶

C.碱性磷酸酶及其同工酶

D.丁-谷氨酰转移酶及其同工酶

E.氨基转移酶及其同工酶

Which of the following statements is tree about his friend().

A.Writing exhausts his friend.

B.His friend collects a lot of things to write.

C.His friend always has enough material to write on.

D.His friend is doing research to write a paper.

水源卫生流行病学侦察的主要内容有哪些？