Question 171·Hard·Form, Structure, and Sense
Although the latest climate models, which incorporate sophisticated feedback mechanisms and machine-learning algorithms, ______ promising results, many scientists caution that substantial uncertainties remain.
Which choice completes the text so that it conforms to the conventions of Standard English?
For subject-verb agreement questions, first strip away any extra phrases set off by commas or dashes to reveal the core subject and verb. Decide whether the subject is singular or plural, then immediately eliminate any choices whose verbs don’t match that number (watch the -s ending on present-tense verbs and singular helpers like "has" and "is" vs. plural "have" and "are"). Finally, among the remaining choices, pick the verb tense and aspect that best fits the time frame and meaning of the sentence.
Hints
Find the subject of the blank
Cover up the phrase between the commas ("which incorporate sophisticated feedback mechanisms and machine-learning algorithms") and see what the main subject of the clause is.
Decide if the subject is singular or plural
Ask yourself: does the key noun before the blank refer to one thing or more than one thing? That will determine whether you need a singular or plural verb form.
Use the -s ending as a clue
Remember that in the present tense, a verb with an -s ending (like "yields") is usually singular (he/she/it yields). Plural subjects (they) usually take the base form without -s (they yield) or a plural helping verb (they have / they are).
Check the time frame
Notice that scientists "caution" now and uncertainties "remain" now. Think about which verb form best shows that the models have already produced results that still matter in the present.
Step-by-step Explanation
Locate the clause with the blank
Focus on the part of the sentence that contains the blank:
"Although the latest climate models, which incorporate sophisticated feedback mechanisms and machine-learning algorithms, ______ promising results, many scientists caution that substantial uncertainties remain."
The verb you choose will complete the clause that starts with "Although."
Identify the true subject of the verb
Ignore the descriptive information between the commas ("which incorporate sophisticated feedback mechanisms and machine-learning algorithms"). That part is extra information.
What is left is:
"Although the latest climate models ______ promising results, ..."
So the subject of the verb is "the latest climate models", which is plural (models, not model).
Match the verb to a plural subject
In standard English, a plural subject needs a plural verb.
Check each option for whether it is singular or plural:
- "has yielded" – uses has, a singular helping verb
- "yields" – the -s ending on a present-tense verb usually marks it as singular (he/she/it yields)
- "is yielding" – uses is, a singular helping verb
All three of these use singular verb forms, which do not agree with the plural subject "models." That means they cannot be correct.
Confirm agreement and tense for the remaining option
The only remaining choice uses a plural helping verb and forms the present perfect tense, which describes an action that started in the past and has results that continue into the present.
This fits the meaning: the models up to now have produced promising results, yet "uncertainties remain" now.
Therefore, the correct answer is "have yielded".