What is considered the "implicit guarantee" that existed between the GSEs and the U.S. government?

Purchasers of GSE mortgage backed securities pay a premium because they have a contract with the government that mandates they will be bailed out if the GSEs were to become unable to meet their obligations.

Purchasers of GSE mortgage backed securities believed that if the mortgages defaulted and the GSEsbecame insolvent, the government would loan the GSEsmoney.

The government issued a set of special one-time Treasury bonds to infuse capital into the GSEs, these bonds have since defaulted.

The government guaranteed that that GSEs would remain a privately held corporations.

None of the above.