A verb agreement question tests whether a verb matches its true subject. Sort the verb forms by whether they go with it or they, then read the sentence around the blank. Set aside information between commas and ask who or what the verb is about. One thing takes a singular verb, and more than one takes a plural verb. Match the true subject, because nouns inside the added information don't decide the verb's number.
Hints
- Hint 1
Look at the part beginning with Although and ask what produces the promising results.
- Hint 2
Mentally remove the words between the first two commas. Does the remaining subject stand for one thing or more than one?
Step-by-step
Sort, find the subject, and match
Step 1Sort the forms by number
Try the verb forms after it and they: this blank needs a verb that matches its subject. The forms has yielded, yields, and is yielding fit after it, so they're singular. Their tenses differ, but number comes first because changing tense can't fix a mismatch with the subject. The blank is in the part beginning with Although, so its subject must come from that part, not from many scientists caution.
- Step 2
Read past the describing clause
What produces the promising results? The words which incorporate sophisticated feedback mechanisms and machine-learning algorithms have their own subject and verb, so they form a clause that describes the models. Its verb tells us what the models include, but the blank needs a separate verb to tell us about their results. Because this describing clause is added information between commas, we can mentally remove it without changing who or what produces the results. That leaves the latest climate models as the true subject of the verb at the blank.
- Step 3
Match the plural subject
Does the latest climate models become it or they? It names more than one model, so we use they and a plural verb. When a verb has a helper, that helper shows its number: have fits they, while yielded stays unchanged. That makes have yielded the form that agrees with the models in this sentence. Choice C.