Option c meets the meaning of the question: secondary investment refers to the investment of the parent fund in the surviving fund or its portfolio company after the establishment of the equity investment fund. (item c is in line with the meaning of the question)

Direct investment refers to the direct equity investment of the parent fund. In practice, the parent fund usually invests with the equity investment fund it invests in, and the parent fund often plays the role of a follower, allowing the equity investment fund to manage this investment. (item a does not meet the meaning of the question)

Primary investment means that the parent fund invests in the equity investment fund when it is raised and becomes a fund investor. (item b does not meet the meaning of the question)

Investment capital refers to the book value of all funds invested by all investors in enterprise operation, including debt capital and equity capital. (item d does not meet the meaning of the question)