1. Most of people invited to the reception were old friends.

2. My parents are sure that my sister will pass the entrance exam to university of this school. 

3. In order to reduce pollution,  public buses should be used instead of motorbikes.

II.

1. He has worked for the same company since he leaved school.

leaved => left

I.

1. Most people invite reception to old friends.

2. My parents are sure that my sister will pass the university entrance exam at this school.

3. In order to reduce pollution public buses should be used instead of motorbikes.

II.

1. He has worked for the same company since he left school.( QK của leave là left)