When answer choices contain multiple punctuation decisions, classify every clause before evaluating individual marks. Then check whether interrupting words such as “however” must be set off on both sides; eliminate any choice that handles only one boundary correctly.
Hints
- Hint 1
Find the main clauses
Determine whether each unit on either side of the first punctuation mark can stand as a complete sentence. Remember to consider the entire first unit, including the clause following “Because.”
- Hint 2
Examine the interrupter
Consider whether “however” is essential to the clause’s grammatical structure or interrupts an otherwise complete subject-verb connection.
- Hint 3
Check both decisions
An option must correctly punctuate both the boundary between the clauses and the word interrupting the second clause.
Step-by-step
- Step 1
Identify the complete clauses
The first unit is a complete clause: “Because the furnaces reached slightly different peak temperatures, Okafor initially expected each sample to develop a distinct microstructure.” Although it begins with a dependent clause, it also contains the independent clause “Okafor initially expected each sample to develop a distinct microstructure.”
- Step 2
Punctuate the clause boundary
The next unit—“electron microscopy, however, revealed the same crack-diverting feature in all three”—is also an independent clause. A semicolon can join these two closely related independent clauses, whereas a comma alone would create a comma splice.
- Step 3
Set off the interrupting adverb
In the second clause, “however” interrupts the connection between the subject “electron microscopy” and the verb “revealed.” It must therefore be set off with a comma before it and a comma after it. Only choice D handles both boundaries correctly.