Which of the following statement(s) is/are incorrect about the risk-free asset?

A T-notes are considered risk-free in practice because the government always guarantees the payment when due.

B In practice, T-bills are considered as "risk-free."

C Money market funds that invest mainly in T-bills are usually considered as "risk free."

D A default free guarantee (such as a T-bond) is a necessary, but not sufficient condition to make an investment risk free.