A verb tense question tests when something happens using different forms of one verb. Check that each form agrees with the subject, then look for a time clue near the blank. Facts use the simple present, past changes linked to now use has, future events use will, and things underway use is with -ing. Without a time word, match nearby verbs describing the same event or process. A tense shift needs a reason in the text.
Hints
- Hint 1
Find the verb paired with the blank in the second sentence.
- Hint 2
Read the first sentence for time clues. Is it about one event at a certain moment, or how this type of engine works?
- Hint 3
Compare the timing of the two benefits. Does the text give a reason for them to use different verb tenses?
Step-by-step
Follow the time clues
Step 1Find the subject and paired verb
This process is the subject of the verb in the blank, and all four choices work with that singular subject, so the time decides. What verb is the missing one paired with? The structure not only improves fuel efficiency but also ______ links two benefits of the same process. Let’s use the verb for better fuel efficiency as our starting point, then check for a reason to change its tense.
- Step 2
Read the description for time
Does the passage describe a particular event or how engines work in general? The first sentence says a gasoline engine relies on spark ignition and a diesel engine compresses air in the cylinder. Those are simple present verbs, which tell us what these engines do as a rule. The second sentence has no date or other time clue that changes when these benefits happen, so both benefits are stated as general facts, not as changes underway at one particular moment.
- Step 3
Choose the form for a general fact
Has enhanced needs a past change linked to now, and will enhance needs a future clue; the passage gives neither. Is enhancing describes something underway now rather than the regular effect stated by improves fuel efficiency. Which form states that second effect as a general fact? The simple present form enhances does, and it matches the verb for the first benefit. Choice D.