Complete the sentences with words below. Each word will be used only once, · trapped · level · plants · average · release · liquid · lack · environment 1. Water is a(n) ______ that humans and other animals need to live. 2. When the ______ of air pollution is very high, cars are not allowed to drive into the city center. 3. As it is now, the ______ on Mars is not suitable for human life. 4. The ______ temperature of Mars is much lower than Earth's. 5. On Earth, there is fresh water ______ in ice. 6. Carbon dioxide is something ______ need to make food. 7. Plants ______ oxygen into the air, making it possible for humans to breathe. 8. The ______ of rain these past few months has made the earth dry.