Lower-Grade Bonds Offer Higher Returns Than High-Grade Bonds Because Of

Lower-grade bonds offer higher returns than high-grade bonds because of:

A) their increase in coupon interest rate over the life of the bonds.
B) their higher risk and more restricted market.
C) their maturity value being higher than the market value.
D) their attractive returns to risk-averse investors.
E) their tax-free returns and no capital gain tax liability.