A verb form question tests whether the blank needs a main verb or a form that only describes. Sort the forms: a main verb says what the subject does or is, and an -ing form needs a helper to be one. Then read to the period, because a long sentence may put its main verb late. Count the main verbs for the blank’s subject, leaving out verbs in other clauses. A second main verb for the same subject needs a joining word.
Hints
- Hint 1
Start with the study sentence and read all the way to the period. Which noun is the subject attached to the blank?
- Hint 2
Set aside the part introduced by whether. Check whether the botanists already have a main verb outside that part of the sentence.
Step-by-step
Find the botanists’ main verb
Step 1Find the subject and sort the forms
The subject in a group of botanists _____ to determine is the group of botanists. The blank could be their main verb, the verb that says what they do, or a form that only describes them, so we need to count their main verbs. As we sort the choices, remember that an -ing form needs a helper to be a main verb.
- Step 2
Read past the long middle
Read past the long middle to placed artificial spines. Who placed them? The botanists did, so placed is their main verb. The verb guide belongs to whether tiny grooves on cactus spines guide water toward the plant’s stem, where the grooves are the subject, and to determine is a to form, not a main verb. The botanists already have their main verb, and no joining word or new clause allows another one in the blank.
- Step 3
Choose the form that describes the group
Had attempted and was attempting would add main verbs for the group without a joining word. Could attempted only describe a group of botanists? Try the was test by adding was: the group was attempted to determine makes no sense, so it also acts as a main verb here. The group does the trying, so attempting describes their goal without adding a second main verb. Choice A.