Why Are the Class C Bonds Highly Attractive to Insurance

Why are the class C bonds highly attractive to insurance companies and pension funds?

A) Because of their ability to offer perfect prepayment protection.
B) Because of the shortest average life with a minimum of prepayment protection.
C) Because of their long expected duration.
D) Because they are basically zero coupon bonds and hence carry a minimum amount of risk.
E) Because of their ability to offer perfect prepayment protection, and because they are basically zero coupon bonds and hence carry a minimum amount of risk.