Answer: Martin Luther King Jr. was an American minister and activist for civil rights in the 1950s and 1960s.
Explanation:
A simple sentence is made up of an independent clause along with one single subject and a verb with a compliment.
In the first option, there is a single independent clause which is that MLK was an American ministers and activist. The subject is MLK and the verb and compliment are the years he was active.
The other options have multiple clauses.
In-text citations: Author-page style. MLA format follows the author-page method of in-text citation. This means that the author's last name and the page number(s) from which the quotation or paraphrase is taken must appear in the text, and a complete reference should appear on your Works Cited page.