根据句意和汉语注释，在相应的横线上，写出单词的正确形式。
It is not polite to laugh at others’ ________ (缺点), boys and girls.
It is ________ (确信的) that the government will take action to prevent the environment getting worse.
Last spring, the viruses ________ (扩散) all of the town in a very short time.
The scientists are devoting themselves to ________ (开发) plants that can grow on Mars.