A verb form question tests whether a sentence needs a main verb or a form that only describes. Sort the forms, then find the subject and count its main verbs through the period. A sentence needs a main verb saying what its subject does or is. After a comma, an -ing form can describe a result, while a to form can show a purpose. Another main verb needs a joining word, unless it has its own subject and punctuation joins the two clauses.
Hints
- Hint 1
Look for the subject and main verb before the phrase about labeling. Which words tell you who did what?
- Hint 2
What does thereby, meaning by doing that, tell you about how the final phrase connects to the display?
Step-by-step
Count the main verbs, then check the meaning
Step 1Sort the forms and find the main verb
Sort the forms by whether they can be main verbs: -ing and to forms can't be main verbs on their own. Now read students displayed models of the solar system. The subject is students, and its main verb is already there, displayed.
- Step 2
Check whether another main verb can fit
Does anything after displayed allow another main verb? Read to the period: each carefully labeled describes the models, and no joining word introduces the blank. Demonstrate would add a second main verb without a joining word, and demonstrated would too. To test whether demonstrated could describe the students, try adding were: students were demonstrated their understanding doesn't make sense, because the students show their understanding of planetary orbits. So the blank must describe, not add another main verb.
- Step 3
Identify what the final phrase adds
What does thereby, meaning by doing that, tell us about the final phrase? It tells what the display showed about the students, so the blank describes a result. To demonstrate would say why they displayed the models, but thereby points to what came from that display. The -ing form demonstrating expresses that result. Choice A.