Select the most appropriate option to fill in the blank.

Everyone knows that the future of all life on earth will be _________ if people don’t control the contamination of the environment.

endangered

The most appropriate option to fill in the blank is endangered.

The sentence is about the future of all life on earth, and how it will be in danger if people don't control the contamination of the environment. The word "endangered" means "likely to become extinct." So, the future of all life on earth will be in danger of becoming extinct if people don't control the contamination of the environment.

The other options are not as appropriate.

• Dangerous means "likely to cause harm." This is not as strong as "endangered," and it does not convey the sense of urgency that the sentence is trying to express.
• Dangered is the past participle of the verb "to endanger," which means "to put in danger." This is not as appropriate as "endangered," because the sentence is talking about the future, not the past.
• Danger is a noun that means "a risk or threat." This is not as appropriate as "endangered," because the sentence is talking about the future of all life on earth, not a specific risk or threat.