1. What was his ____ (反应) to your answer?

2. We have bought lots of ____ (设备) for our new lab.

3. The lock has ____ (生锈) and needs oil.

4. I came to the ____ (结论) that he had been lying.

5. He kept his ____ (平衡) with his arms on top of the wall.

6. The ____(沸腾的) kettle was giving off steam.

7. As a result of pollution，there are many dead fish ____ (漂浮) on the water.

第六次全国人口普查数据显示，我国人口约为13.4亿人，那么我国的人口密度约是（　　）

随着学技术的发展和环保要求的不断提高，CO₂的捕集利用技术成为研究的重点．完成下列填空：

如图，⊙O的直径AB=4，点C在⊙O上，如果∠ABC=30°，那么AC的长是(   )