Answer:
a. It could be less than, equal to, or greater than 6%.
Explanation:
The attribute with related to the second bond i.e. converted and the feature of the sinking fund would be disposed off to decrease the required rate of return on the other hand feature of the call increase the required rate of return on the bond. Also it contains the low coupon rate as compared with the bond i.e. not convertible
Hence, the correct option is A.