The correct answer is D. Concept
Explanation:
In language, the correct form of a word depends mainly on the context in which the word is presented and the meaning this conveys. In the case of the sentence "At first, the group of investors were not impressed by young Calvin's ________ for the new advertising campaign, but by the end of the presentation, everyone was on board with the plan" the missing word should be a subject because it refers to one invention, plan or idea of Calvin. This implies the word that fits in this context is "concept" because this is a noun, while conceive, and conceiving are verb forms that can be used as action in a sentence and conceivable is an adjective that can be used only to describe a noun.
