$6.$ Which of the following statements is true?Ja$.$ Treasury bonds have zero default risk.b$.$ The longer the maturity of a bond, the less risky it is$..$ The real risk$-$free rate incorporates an inflation premium.d$.$ Liquidity premium is included only for highly liquid securities$.$e$.$ The default risk is greater for AAA$-$rated corporate bonds than for BBB$-$rated bonds with the same features