Ответ:

I.

1) If you drop an apple, it falls.

2) I get tired if I work too much.

3) Water boils if you heat it to 100° C.

4) I will phone my friend if I have time today.

5) If you freeze water, it turns into ice.

6) If it rains today, I will stay at home.

7) If I see you tomorrow, I will buy you a drink.

8) We will go to the beach if it is warm tomorrow.

II.

boil - will turn  

was - would take  

put - goes  

put - floats  

was - wouldn't exist  

were - would you fly  

would pass - studied  

heat - melts  

would not do - were  

get - will take  

get - will have to  

turns