消防艇的种类繁多、型号各异，按排水吨位划分，大型消防艇的排水量在()以上。（A）40

---Could you please go skating with us this Sunday?

---____. I have to finish my homework

A．Yes, sure

B．I am sorry

C．Excuse me

D．Good idea

—You didn’t have so much time, did you?

_______. I had nothing to do all day.

A．Yes, I did

B．Yes , I didn’t

C．No. I didn’t

D．No. I did

下列图象与所属实验现象相符的是（  ）

我国合同鉴证制度实行的是（）原则。

A．强制鉴证

B．不必鉴证

C．统一鉴证

D．自愿鉴证

给水加氨处理的主要目的是：提高给水的pH值，防止产生游离二氧化碳的酸性腐蚀。（）