Question 48·Hard·Boundaries
Geophysicist Marcia McNutt recounts in her memoir the moment she first descended into the Mariana Trench, describing the submersible— ______ —as “a fragile soap bubble drifting through midnight,” a metaphor chosen to convey both the machine’s vulnerability and its grace.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation-and-boundaries questions, first strip the sentence down to its main structure to see how the clauses fit together. Identify any existing punctuation (commas, dashes, parentheses) around the blank and decide what kind of phrase is being inserted (essential vs. nonessential, renaming vs. separate clause). Then quickly eliminate choices that double up or mix punctuation (like adding extra dashes or unnecessary commas where another punctuation mark is already doing the job). Between remaining options, prefer the simplest choice that keeps the sentence clear, grammatically correct, and consistent with the idea of essential vs. nonessential information.
Hints
Look at the punctuation already in the sentence
Focus on the part "describing the submersible— ____ —as." What punctuation marks are already around the blank, and what do they usually do in a sentence?
Think about what belongs between the em dashes
The words between the dashes should form one clear phrase that renames or describes "the submersible." Ask yourself: should that phrase be broken up further by more dashes or separated by commas?
Consider whether the description is essential or extra
Is "scarcely wider than a minivan" giving crucial identifying information about the submersible, or is it just an extra comment? Your answer will help you decide whether a comma inside the dashed phrase makes sense.
Step-by-step Explanation
Understand the sentence structure
Read the core of the sentence without the interrupting phrase:
"Geophysicist Marcia McNutt recounts in her memoir the moment she first descended into the Mariana Trench, describing the submersible … as 'a fragile soap bubble drifting through midnight.'"
The blank is inside a pair of em dashes:
"describing the submersible— ____ —as …"
So whatever fills the blank must be an interrupting phrase that renames or describes "the submersible."
Recognize the role of the em dashes
The em dashes already set off the entire description of the submersible as an appositive (a renaming phrase). That means:
- The whole phrase inside the blank should be one continuous description.
- We generally should not add more em dashes inside this already "dashed-off" part.
Check the choices for any options that create double or nested dashes.
Eliminate choices with extra dashes
Look at which options add em dashes beyond the ones already in the sentence:
- Choice B ends with an em dash: "a bathyscaphe scarcely wider than a minivan—".
- Plugged in, that would give: "submersible— a bathyscaphe scarcely wider than a minivan— —as …" with two dashes in a row, which is incorrect.
- Choice C has an internal em dash: "a bathyscaphe—scarcely wider than a minivan".
- Plugged in, that would give: "submersible— a bathyscaphe—scarcely wider than a minivan —as …," creating nested dashes and chopping the description into awkward pieces.
Both B and C misuse the em dash and can be eliminated.
Decide between comma vs. no comma inside the dashed phrase
Now compare the remaining options:
- Choice A: "a bathyscaphe, scarcely wider than a minivan"
- Choice D: "a bathyscaphe scarcely wider than a minivan"
The phrase "scarcely wider than a minivan" is an essential description that tightly defines the type of bathyscaphe being discussed, not a nonessential side note. Essential modifiers are not set off by commas.
So the best version keeps the noun and its essential description together with no extra comma: "a bathyscaphe scarcely wider than a minivan", which makes Choice D correct.