For a challenging boundaries question, trace the full hierarchy of clauses rather than judging only the words nearest the blank. In particular, identify complementizers such as “that” and subordinators such as “because”; then determine whether the material on each side of a proposed mark is independent or dependent before choosing among a comma, semicolon, period, and colon.
Hints
- Hint 1
Find the hypothesis
Identify all the words that belong to the prediction introduced by “had hypothesized that.”
- Hint 2
Examine the opening word
Determine whether the clause beginning with “because” can stand alone or must connect to another clause.
- Hint 3
Test each boundary
For each stronger punctuation mark, check whether all the material before it forms a complete sentence in the surrounding syntax.
Step-by-step
- Step 1
Map the sentence structure
The verb “had hypothesized” introduces a that-clause: “that because the layered fibers retained moisture, oxygen from the surrounding air would not reach the tissue.” The entire prediction is contained within this embedded clause.
- Step 2
Identify the dependent clause
“Because the layered fibers retained moisture” is a dependent clause. Within the that-clause, it comes before the main clause “oxygen from the surrounding air would not reach the tissue.”
- Step 3
Place the boundary
A comma separates the introductory dependent clause from the main clause that follows. Therefore, “moisture, oxygen from the surrounding air” correctly completes the sentence.