A verb form question tests whether the blank says what the subject does or only describes it. Find the subject, then read through the whole sentence, even when extra words sit between commas. Count that subject's main verbs, the verbs that say what it does or is. If there's no main verb, the blank must add one; if there's already one, another needs a joining word. Test each form to see whether it adds a main verb or describes the subject.
Hints
- Hint 1
Find the subject after the opening phrase. Which verbs belong to that subject, and which belong to someone or something else?
- Hint 2
Read beyond the long phrase between commas, looking for what the illustration does.
- Hint 3
Check the words joined by and. What form do the words after and take?
Step-by-step
Find the main verb, then match the description
Step 1Find the blank's subject
Created before astrophotography became widely practical describes when the illustration was made; became belongs to astrophotography. The subject, or what the sentence is about, is each illustration in a nineteenth-century astronomical atlas, so the blank's verb belongs to the illustration. We're choosing a verb form, so we need to find this subject's main verb, which says what it does or is.
- Step 2
Read to the main verb
Read past the words between commas to preserves details. What preserves those details? The illustration does, so its main verb is already there. In its artist recorded and a single viewing might have missed, the verbs belong to the artist and the viewing. These clauses, groups of words with their own subjects and verbs, describe the notes and details.
- Step 3
Rule out a second main verb
Could the blank need its own main verb? No word such as which opens a new clause at the blank, and no and joins it to preserves details. The blank must describe the illustration, so draws on, drew on, and has drawn on can't work: each adds a second main verb for the same subject.
- Step 4
Match the paired forms
With and incorporating color notes, what must the first description match? It must match the -ing form incorporating, because and joins two descriptions of the same illustration. Drawing on means using something as a source, so it describes how the illustration uses observations made on several nights. Choice A.