A punctuation question with extra information tests whether you can separate a side detail from the sentence around it. Read the words on both sides of the blank, and ask where the main sentence picks up again. Cross out the side detail to check that what's left is a complete sentence. Extra information inside a sentence needs matching marks at both ends, while a detail at the sentence's edge needs only one. Match the marks only after finding the detail's full length.
Hints
- Hint 1
Read the words on both sides of the blank. Who is proceeding across the plateau?
- Hint 2
Try removing the words describing the lake. Do the remaining words still make a full sentence about the expedition?
- Hint 3
Once you've crossed out the lake description, find where the expedition's sentence picks up again. If extra information sits inside a sentence, its opening and closing marks must match.
Step-by-step
Find the insert and match its marks
Step 1Follow the expedition's sentence
The words The expedition paused at tell us the expedition stopped somewhere, and each choice gives Lake Vostok as that place. Who is proceeding across the plateau? It's the expedition, so this punctuation question needs to keep the lake's description separate from what the expedition did.
- Step 2
Cross out the lake detail
The words its frozen surface concealing switch from the expedition to a detail about Lake Vostok. Can we remove that detail without breaking the sentence? Cross it out, and we get: The expedition paused at Lake Vostok before proceeding across the plateau. That works, so the lake description is an insert, extra information the sentence can do without. It ends after water, where before brings us back to the expedition's next move.
- Step 3
Test the paired marks
Which marks can frame the insert while the sentence carries on with proceeding across the plateau? An insert inside a sentence needs matching marks at both ends. The version with a comma then a dash mixes the marks, and the version with a dash then a comma makes the same mismatch in reverse.
- Step 4
Close both ends
The version with only an opening comma leaves the lake description without a closing mark. That description comes before proceeding across the plateau, which returns to the expedition's journey, so it isn't a detail at the sentence's end. The version with two dashes sets off the whole description and lets before connect the expedition's stop to its next move. Choice B.