Question 210·Hard·Boundaries
In an effort to improve flight efficiency, engineers examined the aerodynamic performance of owl wings; the results revealed that microstructures along the leading edge reduce _____ a discovery that could inform the design of quieter aircraft.
Which choice completes the text so that it conforms to the conventions of Standard English?
For sentence-boundary and punctuation questions, first isolate what comes before and after the blank. Test the part after the blank: if it cannot stand alone as a complete sentence, eliminate semicolons and periods, which require full sentences on both sides. Then decide whether the second part is extra descriptive information (often set off with a comma) or something that should be tightly connected without a pause. This quick check of clause type and relationship will usually point you to the correct punctuation choice within seconds.
Hints
Look closely at what follows the blank
Focus on the words after the blank: "a discovery that could inform the design of quieter aircraft." Think about whether this feels like a full sentence on its own or more like a phrase describing something.
Recall when to use semicolons and periods
Semicolons and periods are used to separate two complete sentences. Ask yourself: can the part after the blank stand completely alone as a sentence if you started with a capital letter there?
Check how the second part relates to the first
Is the phrase after the blank adding extra information about the result that was revealed, or is it introducing a brand-new, separate statement? Your punctuation should match that relationship.
Step-by-step Explanation
Identify the two parts around the blank
Read the sentence up to the blank:
"...the results revealed that microstructures along the leading edge reduce turbulence _____ a discovery that could inform the design of quieter aircraft."
Before the blank, we have a complete idea: "the results revealed that microstructures along the leading edge reduce turbulence". After the blank, we have the phrase "a discovery that could inform the design of quieter aircraft." Our job is to see what role this second part plays and what punctuation correctly links it.
Decide what kind of phrase comes after the blank
Ask: Can "a discovery that could inform the design of quieter aircraft" stand alone as a complete sentence?
It cannot, because it is a noun phrase (it names something: a discovery) with extra description. It does not make a full statement like "It is a discovery" or "This discovery could inform..." on its own. That means it is not an independent clause (not a full sentence by itself).
Match the phrase to the punctuation rule
Semicolons and periods must be followed by a complete sentence. Since the words after the blank are not a complete sentence, we cannot use a semicolon or a period there.
Now compare the other two options: using no punctuation or using a comma. Without any punctuation, we get "reduce turbulence a discovery that could inform...", which is ungrammatical and hard to read. Instead, English normally uses a comma to set off a noun phrase that renames or explains the entire idea before it (an appositive).
So the correct punctuation after "turbulence" is a comma: the sentence should read "reduce turbulence, a discovery that could inform the design of quieter aircraft." The correct answer is D) turbulence,.