If it's your friend's birthday, you ...
you will / you'll
If it's your birthday, ...you ?? eat at an expensive restaurant
can ...
If I don't understand something in my English class, I ...
I will / I'll
If I get lots of homework today, I ...
I will / I'll
If I get up early tomorrow, ....
I will / I'll ...
If I have some free time on Saturday, ...
I will / I'll ...
I ..... if it's sunny tomorrow.
I will ... / I'll ....
If I can't fall asleep tonight, I ...
I will ... / I'll ....
If I get fatter, I ...
I will / I'll
If I feel sad about something, ...
I will ... / I'll ....