Chris is the head of Superstar Inc. He has decided to expand the company's operation by issuing bonds. He is uncertain about the cost and benefits of certain bond features. He is not sure how each feature would affect the bond holders' required rate of return. Please help him prepare a memo to describe how each feature below (given other features are the same) would potentially impact the bond holder's required rate of return:

1) callable vs. noncallable bond

2) bonds with sinking fund vs. without sinking fund.

3) bonds with AAA rating vs. BAA rating

4) convertible bond vs. straight (non-convertible) bond