可以统称为核子的是（）
A.氢原子
B.氦原子
C.氧原子
D.质子和中子
E.电子和光子
参考答案：D
解析：质子和中子统称为核子。
---Could you tell me ?
---Sorry, I have no idea. I wasn't at the party.
A．what does she say at the party
B．what did she say at the party
C．what she says at the party
D．what she said at the party
根据污水中可沉淀物的性质，凝聚性能的强弱及其浓度的高低，沉淀可分为哪几种类型？各自的特征是什么？
