A punctuation question tests where sentences meet and how their ideas connect. Split at the blank, then ask whether each side can stand alone, saying who or what it’s about and what it does or is. Two full sentences need a boundary, not a comma alone or no mark. A semicolon joins full sentences; a colon follows one and introduces a list or an explanation of it. With an earlier view and a newer finding, check how the ideas connect.
Hints
- Hint 1
Fill in the word all the choices share and test each side as its own sentence. Does each side say who or what it’s about and what it does or is?
- Hint 2
Compare the earlier assumption and the newer finding. What do the words primarily and may also tell you about how those ideas connect?
Step-by-step
Test the sentences and their connection
Step 1Test the first side
Fill in camouflage, which every choice shares, and split the text right after it to test the punctuation. Does the first side stand alone? Researchers long assumed gives us a subject, who the words are about, and a main verb that says what they did. The that part tells us what they assumed about the skin, so the whole first side is a full sentence.
- Step 2
Test the second side
Does the second side have its own subject and main verb? recent studies reveal gives us both, and the rest tells us what those studies reveal. This side can stand alone too, so the version with a comma makes a comma splice, which joins two full sentences with only a comma. The version with no punctuation leaves them running together without a boundary.
- Step 3
Check what the newer finding does
served primarily as describes the old assumption, while may also facilitate thermal regulation introduces the newer finding. Does the newer finding explain that assumption? No, it adds another possible job for the skin rather than explaining why researchers thought camouflage was its main role. A colon needs what follows to list or explain the statement before it, so the colon doesn’t fit the link between these ideas.
- Step 4
Join the two sentences
A semicolon can join two full sentences even when the second doesn’t explain the first. The version camouflage; puts that boundary between the researchers’ earlier assumption and what recent studies reveal, so the two full sentences are joined correctly. Choice D.