In certain Structure items, the correct use of parallel structures is tested. Parallel structures have the same grammatical form and function. Look at the following sentences:
She spends her leisure time hiking, camping, and fishing.
He changed the oil, checked the tire pressure, and filled the tank with gas.
Nancy plans to either study medicine or major in biology.
Nancy plans to study either medicine or biology.
All of the structures in italics are parallel. In the first, three gerunds are parallel; in the second, three main verbs; in the third, two simple forms; in the fourth, two nouns. Many other structures must be parallel in certain sentences: adjectives, adverbs, infinitives, prepositional phrases, noun clauses, and others.
The most common situation in which parallel structures are required is in a sequence (A, B, and C) as in the first two sentences above. Parallel structures are also required with correlative conjunctions such as either . . . or or not only . . . but also. (Correlative conjunctions are presented in Lesson 30.)
∇ Sample Item
San Francisco has a pleasant climate, ________________ and many fascinating neighborhoods.
(A) exciting scenery,
(B) has exciting scenery
(C) that the scenery is exciting
(D) the scenery is exciting,
This sentence contains a series of three objects after the verb has: the first and third are noun phrases (a pleasant climate and many fascinating neighborhoods). To be parallel, the second object must also be a noun phrase. Therefore, choice (A) is the correct answer; (B), (C), and (D) are not parallel.