3.I decided not to tell the secret.

5.I decided not to help my friend do homework.

8.I decided not to believe the rumor.

9.I decided not to work for a while.

10.I decided not to study math  for a while.

2.Why decide togo fishing?

3.Why did you decide to quit school?

4.Why did you decide to use a credit card?

5.Wht did you decide to participate this competition?

7.Why did you decide to cheer for Korean football team?

8.Why did you decide to come here suddenly?