Complete the sentences with the correct form of the verbs in parentheses. 

1. Polar bears _____ (lose) their habitat if the sea ice _____ (melt).

2. If we _____ (take) action now, we _____ (help) protect nature.

3. If the temperature _____ (get) higher, more wild animals _____ (be) endangered.

4. Polar bears _____ (try) to find food in towns if they _____ (have to) live on land.

5. If humans _____ (not control) climate change, more species _____ (become) extinct.