An argument that is missing a part--either a premise or a conclusion--is called ... a. An extended argument. b. An incomplete argument. c. An enthymeme. d. A fallacy.

option C

Explanation:

An argumentative assertion wherein the author or spokesperson ignores one of the large or small assumptions, does not express it explicitly or suggests this assumption is called an "enthymeme." Nevertheless the excluded premise in an enthymeme remains recognizable even though it is not articulated clearly.

Enthymeme is a rhetorical device such as syllogism, and is known as truncated syllogism or rhetoric. The goal is to influence the audience, and make inferences for them. It is easy to recognise such inferences as these comments occur after "because."