Look at the pictures and complete the sentences. Use the zero conditional.

1. If you heat water, it boils
heat / water / it / boil

2. If you
send / an e-mail / it / be / free

3. It
be / dangerous / you / not / wear / a seatbelt

4. If you
have / an injection / it / not / usually hurt

5. If you
not / water / plants and flowers / they die

6. If the sea
not / be / calm / not / be / safe / to swim