问题如下：
What is the mechanism that leads to the share price of an ETF being close to its NAV?
选项：
解释：
Institutional investors have the right to exchange shares in the fund for their share of the assets of the fund. They can also obtain new shares in the fund by contributing to the fund a portfolio that reflects the fund’s current asset mix.
基础班讲义有但我没找到老师解析这句话，这句话如何理解？
