2001年缸盖的清洁度控制限值是（）。 A.≤30mg B.≤40mg C.≤50m

在数轴上表示某数a的点到原点的距离小于2，则a的取值范围为 ______．

补全对话。

Meimei: Hi!

Twins: Hi, Meimei!

Meimei: 1_____ you 2_____ a good time last Sunday?

Lucy: Yes, we did. We 3_____ to the Great Wall.

Meimei: Great! Where did you have lunch then?

Lily: We had lunch at the 4_____ of the Great Wall.

Meimei: What kind of food did you have?

Lucy: I 5_____ Beijing roast duck, but Lily 6_____. She ate fish.

Meimei: How long did you stay there?

Lily: 7_____ about five hours. We took many photos there.

Lucy: What about you?

Meimei: I 8_____ a game with Jim and Tom in the morning. I did my homework in the afternoon.

Lily: Did you 9_____ any English homework?

Meimei: Certainly, I 10_____ to do my English exercises in the evening.

我国土地面临的问题是（　　）

A．近几年来，我国的土地资源没有变化

B．由于大规模地植树种草，使耕地迅速减少

C．由于水土流失、沙漠侵呑、盲目开发，使耕地迅速减少

D．由于大规模地“开源”，使土地面积不断增加

血液与组织细胞进行物质交换的是[ ]

A．心脏

B．动脉

C．静脉

D．毛细血管

促性腺激素的种类及其作用是什么？