With regard to the investment of a fixed annuity's assets, which of the following statements is true?

a$.$ Premiums are invested into the insurer's separate account.

b$.$ Premiums are directed into the insurer's general account.

c$.$ Premiums are invested at the owner's option into either secure bond or fixed interest accounts.

d$.$ Premiums are directed at the owner's option into either government$-$issued Treasury bills or money market accounts.