Callable corporate bonds:

Callable corporate bonds need to be priced lower and therefore yield more to investors as they are likely to be called by the issuer when interest rates fall and the issuer finds it attractive to refinance the debt using new cheaper debt.

They are most unlikely to be called when their prices have fallen because falling prices indicate higher rates, which means the issuer is able to fund himself at a cheaper rate.

Because of their callable feature, they are less convex and may actually carry negative convexity.

Therefore Choice 'b' is the only correct statement and the right answer.