A verb form question tests whether you need a main verb and which subject it must match. Sort the forms, because an -ing or to form can't be a main verb on its own. Then read to the period to find whether the sentence already gives its subject a main verb. With a long subject, cross out added details to find who or what the verb belongs to. Use a singular helper for one thing and a plural helper for more than one.
Hints
- Hint 1
Read the second sentence through to the period. Which verbs belong to smaller parts introduced by how or that, and is there a main verb left for the sentence's subject?
- Hint 2
Look for the word at the heart of the subject. What remains if you set aside the details beginning with of and together with?
- Hint 3
Replace the blank's true subject with it or they. Which pronoun keeps the sentence's meaning, and what form does its helper need?
Step-by-step
Sort, count, and match
Step 1Sort the verb forms
______ enabled researchers puts the blank directly before enabled, so test the two words together. A main verb says what the subject does or is. How do the choices differ? Having is an -ing form, and to have is a to form, so neither can be a main verb on its own.
- Step 2
Find the blank's job
Does the rest of the sentence give The recovery a main verb? The form showing describes the analyses, scatter belongs to how those grains scatter light, and the verb about being lost describes the hues. None is a main verb for the recovery, so the blank must make a main verb with enabled. Having enabled and to have enabled would leave a fragment, a group of words that can't stand alone.
- Step 3
Find the true subject
What enabled the modeling? In The recovery of tiny mineral grains, the words starting with of tell us what was recovered, not what enabled the modeling. The later phrase beginning together with new analyses adds a detail, but together with doesn't join subjects as and does. Cross out these details, and the true subject is one recovery, not the grains, birds, or analyses.
- Step 4
Match the helper
Use it for The recovery and pair it with the helper: it has enabled. The singular helper has matches one recovery and makes has enabled the main verb. Have would give us it have enabled, which doesn't match a singular subject. Choice C.