4) . complete the sentences with the right form of the verb. 1. if we (not stop) global warming, the temperate (rise). 2. unless we (do) something, we (lose) lots of important towns and cities. 3. we (stop) global warming, when we (stop) polluting the air. 4. if each of us (plant) a tree, he (help) our planet a lot. 5. polar ice caps (continue) melting, until every human (start) doing something for our planet.