Almost free points. Easy for native speakers! I'm from Poland - grammar task. Please, help me.

1.) I can understand that some students feel a little homesick in their first week here, it is normal.

2.)  I strongly believe it is important that the children must be taught the difference between right and wrong.

3.)  I can't work out the odd fact that he complained now, right after the end of his course.

4.) Its bewildering to me why she left without saying anything because I'd really like to know.

5.) "Don't let your feelings run away with you, will you?" insisted the youth club leader.

6.) "We must simply go to the police about this latest attack," warned a bystander

Explanation: