Question 162·Medium·Form, Structure, and Sense
Unlike a conventional gasoline engine, which relies on spark ignition, a diesel engine compresses air in the cylinder until it becomes hot enough to ignite the injected fuel. This process not only improves fuel efficiency but also ______ the engine's durability by reducing wear on the ignition system.
Which choice completes the text so that it conforms to the conventions of Standard English?
For verb-form questions in Standard English, first identify the subject and the existing verbs in the sentence to see what tense and aspect are already being used. Then, check for structures like "not only ... but also" that require parallel grammar on both sides. Pick the choice that matches the established tense (often simple present for general facts) and keeps the forms parallel, and avoid unnecessary or un signaled shifts to perfect, progressive, or future tenses.
Hints
Look at the verb already in the sentence
Focus on the verb right before the blank: "improves." What tense and form is that verb in?
Decide the time frame being described
Is the sentence talking about a one-time event, something in the future, or a general fact about how diesel engines work?
Use parallel structure with "not only... but also"
The phrase "not only improves ... but also ___" should use two verbs that match in tense and style. Which option creates the most balanced and consistent pair with "improves"?
Step-by-step Explanation
Identify what grammar issue is being tested
Look at the part of the sentence with the blank: "This process not only improves fuel efficiency but also ______ the engine's durability..." The underlined spot is a verb that must match the grammar and style of the rest of the sentence, especially the verb "improves."
Determine the time frame and style of the sentence
The sentence is explaining how diesel engines work in general. That kind of scientific or technical description usually uses the simple present tense to state general facts (for example, "water boils at 100°C," "a diesel engine compresses air"). We already see this with "compresses" and "improves."
Check for parallel structure with "not only... but also"
The construction "not only ... but also ..." normally connects two parallel grammatical forms. Here, the first verb is "improves" (simple present). The verb in the blank should therefore also be simple present and agree with the singular subject "process" (so it should be in the form "verb + s").
Evaluate the choices and select the verb that matches
Choice A, "has enhanced," is present perfect and does not match "improves" in tense or form. Choice B, "will enhance," is future tense, which does not fit a general present-time fact. Choice C, "is enhancing," is present progressive and breaks the parallel with simple present "improves." Choice D, "enhances," is simple present and agrees with the singular subject "process," keeping the parallel structure: "This process not only improves fuel efficiency but also enhances the engine's durability..." So the correct answer is D) enhances.