The fund embodies a trust relationship and a beneficiary certificate, and investors become the beneficiaries of the fund when purchasing fund shares. Option a is wrong. Securities investment fund is an indirect investment method. Option b is wrong. Closed-end fund means that once the fund is established, the scale of the fund is fixed within the prescribed time limit, and it is impossible to issue additional funds and redeem fund shares. Option c is correct. Open-end fund refers to an investment fund with variable fund size, in which investors can purchase and redeem fund shares at the time and place agreed in the contract after the fund is established. Option d is correct.