Question 25·200 Super-Hard SAT Reading Questions·Standard English Conventions
To determine why an alumina composite remained resistant to cracking after repeated heating, materials scientist Leila Okafor compared samples fired in three furnaces. Because the furnaces reached slightly different peak temperatures, Okafor initially expected each sample to develop a distinct _____ revealed the same crack-diverting feature in all three: a thin glassy layer along each grain boundary.
Which choice completes the text so that it conforms to the conventions of Standard English?
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
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.”
Examine the interrupter
Consider whether “however” is essential to the clause’s grammatical structure or interrupts an otherwise complete subject-verb connection.
Check both decisions
An option must correctly punctuate both the boundary between the clauses and the word interrupting the second clause.
Step-by-step Explanation
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.”
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.
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.