The knowledge point to be investigated in analyzing this problem is the contractual investment fund. Contractual fund is a kind of fund established according to the fund contract. In China, contractual funds are established on the basis of fund contracts signed by fund managers and fund custodians. Fund investors become fund share holders and parties to fund contracts after obtaining fund shares, and enjoy rights and assume obligations according to law. Contract funds rely on the management and operation of fund managers for investment. Therefore, in the operational relationship of contractual funds, fund managers are in the core position. So, the answer to this question is a.