b. garden
A preposition is found in a sentence in which it introduces information to the reader like a location perhaps. The object of the preposition can be a noun, a pronoun or even a gerund that is usually together with the preposition in order to complete a prepositional phrase. In the statement above, the prepositional phrase is "on the garden", therefore the preposition is "on" and the object of the preposition is the "garden" to which the preposition "on" refers to.
A, the passage mainly focuses on the theories and mechanisms of yawning
My answer would be C) encyclopedia.
When you say that phrase, you are saying that you found a fact from a reliable source, such as a website, dictionary, encyclopedia, etc.
