The tourist guide had a vast _______ of knowledge about the city's history.

Concept: In sentence-completion vocabulary questions, the blank must be filled with a word whose core meaning matches the context clues in the sentence. Words meaning "a large collection or store" fit a context signalled by words like "vast", while words meaning "a lack or insufficiency" contradict such a context.

Application: The sentence describes the tourist guide's knowledge as "vast", which signals abundance. Among the options, "repository" means a place or collection where a large amount of information is stored, matching the sense of a vast amount of knowledge.

• "deficit" means a shortfall or lack of something needed, the opposite of the abundance signalled by "vast".

• "shortage" means an insufficient supply of something, again contradicting "vast".

• "scarcity" describes a state of being scarce or in short supply, which also conflicts with the abundance implied by "vast".

Since "repository" alone conveys a large stored collection, it is the option that correctly completes the sentence.