5.People (not/use) petrol soon. aren`t use

won`t use

don`t use

6.

I (stay) at home if it (rain).

will stay, rains
stays, will rain
stay, rain

7.
If it (snow), we (make) a snowman.

snows, will make
snows, makes
will snow, will make

8.If he (eat) so much, he (put) on weight.

will eat, will put
eats, will put
eats, puts
​