The Securities Act of 1933 requires securities offered to the public to be registered with the SEC unless they qualify for an exemption. Open-end investment companies (mutual funds) are not exempt and must register.

D is correct because mutual funds are publicly offered and require registration.

A is incorrect because private placements are exempt under Regulation D.

B is incorrect because municipal securities are exempt under Section 3(a)(2).

C is incorrect because U.S. government securities are also exempt under Section 3(a)(2).