The Primary Difference Between a Mutual Fund and a Closed-End

The primary difference between a mutual fund and a closed-end mutual fund is:

A) mutual fund investors pay loads; closed-end fund investors pay commissions
B) mutual funds share issuance is "open," closed-end funds is generally "closed."
C) the mutual fund usually sells at NAV; closed-end funds at a discount.
D) all of the above are differences between mutual funds and closed-end funds.