用括号中所给单词的适当形式完成下列句子.

1. Joanna received many _________ when graduating from middle school. (gift)

2. Alex is _________ years old and is taken good care of in the kindergarten. (fourth)

3. Whose school uniform is that on the chair, yours or _________? (my)

4. It was _________ for human begins to predict weather in the past. (difficulty)

5. There is a beautiful _________ on the wall in each room of my house. (paint)

6. You need to explain your opinions quite _________ when having a debate. (clear)

7. Let's hope that all our troubles will __________ soon. (appear)

8. The local people are ___________ that the whole nation are helping them rebuild the town. (thank)

小洪同学家原来用液化石油气烧水，每天约用60℃的热水100kg。她参加“探究性学习”活动后，在老师指导和同学帮助下，制作了一台简易的太阳能热水器。

（1）若这台热水器夏天平均每天可将100kg的水从20℃加热到60℃，这些水吸收的热量为多少？

（2）若液化石油气燃烧放出的热量有70%被水吸收，她家改用太阳能热水器后，平均每天可节约液化石油气多少千克？（液化石油气的热值为8.0×10⁷J／kg）