Mortgage bonds have the lowest interest rate and the highest price among the four types of bonds. Because of the fact that mortgage bonds are secured by mortgage liens, the interest rate on these bonds is low and the prices are higher. Options A and D are incorrect because Corporate Bonds offer a higher yield relative to a government bond due to the higher risk of insolvency. Straight-coupon discount bonds are sold at discount prices. Thus, the interest rate on such bonds is high. Option B is also incorrect because debenture issues are unsecured bonds. Due to higher risk, the price of the bonds is lower, and the interest is higher.