The Apollo 11 astronauts _______ of the Earth's inhabitants witnessed on the famous first moonwalk on July 20, 1969, were Neil Armstrong and Buzz Aldrin.

Whom millions

The sentence has a main subject and verb divided by several phrases describing the main subject. After the blank there is the preposition of which leads to believe that a noun should be part of the blank. 1. It is not (A) because a single connector is insufficient. 2. It is not (C) because it has a verb which is not needed. 3. It is not (D) because it has a verb and no noun. 4. It is (B).