A. Commercial paper is not the marketable security with the least amount of default risk. Commercial paper is unsecured and therefore does not have any collateral behind it.

B. Federal government agency securities are backed only by the agency of the U.S. government that issues the securities. Therefore, they have slightly more default risk than securities issued by the full U.S. federal government.

C. U.S. treasury securities are backed by the federal government as a whole and are considered to be the investment with the lowest amount of default risk.

D. Repurchase agreements are not considered the marketable security with the least amount of default risk. If the company involved in the repurchase agreement goes bankrupt, the repurchase agreement loses its value.