Mistakes don’t just happen, but they occur for a reason. What we ought to do is find out the reason and then making the mistakes _____________.

(2009安徽合肥质检)Having failed in many attempts，the bird       managed to escape from the cage．

This book is well worth _______. Would you like to buy one?

 As she is a _____ visitor to our house, we look on her as a part of our family.

Why so many youths are _____ on playing computer games often puzzles us a lot.