A punctuation question with one idea tucked inside another tests whether each part can stand alone. First, compare what the marks need so you know what to check on each side of the blank. Periods and semicolons need complete sentences on both sides, colons need one before them, and commas can attach opening parts that can't stand alone. Then read the whole thought around the blank, including words that make one part depend on another. A subject and verb aren't enough if the thought still needs more.
Hints
- Hint 1
Start at hypothesized that and read through the entire prediction. Which words tell you what Banerjee expected to happen?
- Hint 2
Look for the word that introduces the reason about the fibers. How does that reason relate to what Banerjee predicted?
- Hint 3
Test whether stopping at the blank finishes the thought introduced by that. Having a subject and verb earlier isn't enough if that thought still needs more words.
Step-by-step
Follow the whole prediction
Step 1Check what the sentence marks need
The choices place different marks after moisture, which ends the part beginning the layered fibers retained. What do the period and semicolon need? A period and a semicolon both need full sentences on each side, so let's check whether the words before the blank can stand alone.
- Step 2
Check whether the prediction is complete
Read back to Banerjee had hypothesized that because. Does the part before the blank finish what Banerjee predicted? It doesn't: that introduces the prediction, while because starts its reason about the fibers retaining moisture. The reason still needs the prediction it explains, which follows in would not reach the tissue, with oxygen as its subject. The unfinished prediction rules out the period and semicolon.
- Step 3
Test the colon
What about the version with a colon? A colon needs a complete sentence before it, even if the next part explains something. Here, hypothesized that because the layered fibers retained still leaves the prediction unfinished after moisture, so a colon can't go there.
- Step 4
Close the opening reason
An opening because part takes a comma before the prediction it explains. That pattern also works inside had hypothesized that: moisture ends the reason, and the words about oxygen say it would not reach the tissue. The comma closes the reason within the prediction, so use moisture, oxygen from the surrounding air. Choice C.