22. Space explorers to Mars discover not only life but financial market that are remarkably similar to those on Earth. One type of Martian security issues a fixed number of shares in an IPO and invests the collected funds in a variety of assets. The fund is managed by an investment advisor. Shares in such funds, not redeemable, are traded on the Martian Stock Exchange. One of the human space explorers observes that even though these Martian Investments can be purchased at a discount from their NAV. He tells the rest of his crew that they are a "terrific investment opportunity." He says that they closely resemble which security on earth? a. ETF b. Mutual fund c. Closed-end mutual fund d. Variable annuity