元素周期表的作用与意义：（1）根据元素在周期表中所处的位置，可以预测该元素的     ____  和用途。（2）获取元素的许多信息。

在鱼缸内放一些水草，在阳光照射下，水草会有气泡冒出，这些气泡里的主要气体是 

    Mr. Smith made many tests (作试验) with different animals and the monkey was the cleverest of all the animals. One day Mr. Smith put a monkey in a room. He also put some small boxes in it. In one of the boxes there was some food. "How long will it take the monkey to find the food?" Mr. Smith said to himself. "Let me wait and see." He left the room and waited outside. Three minutes later, he put his eye to the keyhole (钥匙眼). What did he see? He saw the eye of the monkey. The monkey was on the other side of the door and looked at Mr. Smith through the keyhole.