1 we can only if someone has a key

2 if it stops rainning, we will go out

3 water couldn't run down hill if without gravity

4 if you studied hard,you would pass the final examination

5 if you can't understand anything, listen to the teacher's explanation

6 if i didn't go to class, i was sick yesterday

126.We can only get into the house if someone has a key.

127.If it doesn't stop raining,we won't go out.

128.Water couldn't run down hill if it wasn't graviated.

129.If I hadn't studied hard,I wouldn't have passed the final examination.

120.If you don't listen to the teacher's explanation,you can't understand anything.

121.If I hadn't been sick yesterday,I would have gone to class.

122.If Alan ate breakfast,he wouldn't always overeat at lunch.