An agreement question tests whether a verb matches its subject, even when describing words come between them. First, sort the verb forms by number: singular forms fit it, and plural forms fit they, even if their tenses differ. Then ask who or what the verb tells you about, and cross out words that describe that subject. Replace the subject with it or they to check which form it takes. A nearby noun inside a describing phrase doesn't decide the verb.
Hints
- Hint 1
Look at the second sentence and ask what it calls essential for beginners.
- Hint 2
Cross out the phrase that begins with containing. What noun remains as the subject, and would you replace it with it or they?
Step-by-step
Sort, find the subject, and match
Step 1Sort the verb forms
Start by sorting the verb forms by number. Are, have been, and were are plural forms: they fit they, not it. This blank tests subject-verb agreement, which means a verb must match whether its subject is one thing or more than one. The sentence calls something essential for beginners, so let's find what that is.
- Step 2
Find the true subject
What does the sentence call essential? The words containing dozens of intricate diagrams describe what's inside the guide, so we can cross out that whole phrase. That leaves A comprehensive guide next to the blank. The true subject is guide. Diagrams belongs to the crossed-out phrase, even though it's the noun closest to the blank.
- Step 3
Match one guide to its verb
Can we replace A comprehensive guide with it or they? One guide becomes it, so it takes a singular verb. Is fits that subject in the short version: it is essential for beginners. Choice D.