A punctuation question with choices that differ only in marks tests whether sentence parts belong together. Find the main verb, then find its subject: who or what the verb tells you about. Test how the parts join: a colon needs a full sentence before it, a semicolon needs one on each side, and a comma must not separate a subject from its verb. To test a long subject, replace it with it or they.
Hints
- Hint 1
Read from “the reason” through the end of the sentence. Ask whether the words before the punctuation spot could stand alone.
- Hint 2
The sentence contains more than one verb. Look for the verb that tells you what the reason is, rather than stopping at the first verb you see.
- Hint 3
Trace the words beginning with “the reason” and find where the subject ends. How does that subject connect to the words after the blank?
Step-by-step
Test the marks and shrink the subject
Step 1Check for a complete sentence
The sentence's main point begins with the reason, and the choices ask whether a mark should follow their shared word. Can the words before that mark stand alone? They name the reason for the leaves' color, but they haven't yet said what that reason is. A colon needs a full sentence before it, and a semicolon needs one on each side, so the colon and semicolon fail that test.
- Step 2
Find the subject and main verb
Read past the blank to is, the main verb that tells us what the reason is. Why isn't appear the main verb? It describes the leaves in the part about their color, rather than telling us what the reason is. The subject, the words naming who or what the sentence is about, runs from the reason through the word added at the blank. That puts the punctuation spot between the subject and its verb.
- Step 3
Shrink the subject to test the comma
Shrink the long subject to it, and the sentence starts It is instead of using all the words about the leaves. Would you put a comma between it and is? No, because a subject and its verb take no separating comma, however long the subject is. The full subject also leads straight into is that pigments called anthocyanins, so unfurling fills the blank without adding a break before the verb. Choice D.