5. It is necessary to improve the packaging.
改进包装方法十分必要。
还能这样说：
Improving the packaging is necessary.
It is necessary to make the packing better.
应用解析：
improve abilities 提高能力；
improve one's time 善用时间；
improve in health 改善健康

6. We have a big demand for this product.
关于这类产品我们有很大的需求量。
还能这样说：
We need to a big deal of this product.
There is a great demand for this product.
应用解析：
have many demands on one's time 时间不够支配；
in great demand 需要量很大

7. Our toys are lacked variety.
我们的玩具太单一。
还能这样说：
Our toys are too simple.
We don't have various toys.
应用解析：
a variety of 各种各样的，种类繁多的；
every variety of form 各种形式

8. Manufactures are interested in technical improvements.
生产厂商对技术改进很感兴趣。
还能这样说：
Manufactures are fond of the technical improvements.
Manufactures take a great interest in improving the technology.
应用解析：
bear interest 产生利息；提供利息；
give back with interest 连利息一起偿还某人；加倍还击某人