Question 172·Easy·Boundaries
Researchers discovered that the enzyme catalyzes the reaction _____ remarkable speed—more than a million times faster than it occurs without the enzyme.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation “boundary” questions like this, first read the full sentence to understand its structure, then identify whether the words before and after the blank form a single phrase (like a prepositional phrase) or two separate clauses. Apply rules: do not insert commas, dashes, or colons inside a prepositional phrase; colons must follow a complete sentence; and dashes should only be used to set off or introduce extra information. Eliminate any choice that breaks a phrase or violates these rules, and choose the one that keeps the sentence smooth and grammatically complete.
Hints
Look at the words around the blank
Focus on how "the enzyme catalyzes the reaction" connects to "remarkable speed." What kind of phrase describes how it catalyzes the reaction?
Think about prepositional phrases
The word in the blank is a preposition. Should there be any punctuation between that preposition and its object, "remarkable speed"?
Check the rules for colons, commas, and dashes
A colon has to come after a complete sentence. A comma or dash can separate ideas, but here you are inside a phrase. Which choices incorrectly split the phrase?
Step-by-step Explanation
Understand what the sentence is saying
Read the whole sentence:
"Researchers discovered that the enzyme catalyzes the reaction _____ remarkable speed—more than a million times faster than it occurs without the enzyme."
The blank comes right before "remarkable speed," and the dash after "speed" introduces extra explanation: "more than a million times faster..."
Decide what kind of word belongs in the blank
The sentence is describing how the enzyme catalyzes the reaction: it does so at or with remarkable speed. That means we need a prepositional phrase connecting "the reaction" to "remarkable speed" ("the reaction with remarkable speed"). Any punctuation that interrupts between the preposition and its object will be a problem.
Apply punctuation rules to each choice
Check each option in context:
- A) "with— remarkable speed—" would add a dash right after "with" and then use the existing dash after "speed." That creates a pair of dashes around "remarkable speed" for no good reason and makes the structure awkward and unclear.
- B) "with, remarkable speed—" puts a comma between the preposition "with" and its object "remarkable speed," which is grammatically incorrect because it breaks the prepositional phrase.
- C) "with: remarkable speed—" uses a colon after "with." A colon must follow a complete sentence (an independent clause), but a clause ending in "with" is not complete, so this is grammatically wrong.
Choose the option that keeps the phrase smooth and correct
The only option that leaves a smooth, grammatically correct prepositional phrase is D) "with," giving:
"Researchers discovered that the enzyme catalyzes the reaction with remarkable speed—more than a million times faster than it occurs without the enzyme."
So the correct answer is D) with.