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Question

Difficulty: Very hardDashes

Identify the punctuation mark that should fill the blank to ensure the sentence is grammatically correct and consistent.

Answer:Although the standard theory of planet formation suggests that gas giants form far from their host stars—where temperatures are low enough for volatile compounds to condense 【—】 the discovery of 'hot Jupiters' orbiting mere fractions of an astronomical unit from their stars has forced astrophysicists to revise their models of planetary migration.

Answer

A dash (—)
The parenthetical clause detailing where gas giants form ('—where temperatures are low enough for volatile compounds to condense') is opened with an em dash. To maintain grammatical consistency, the clause must also be closed with a dash. A dash is the only punctuation mark that correctly completes this pair.

Step-by-Step Solution

1
Analyze the structure of the sentence, focusing on the parenthetical element setting off the description of where gas giants form.
Identify that the parenthetical clause begins with an em dash ('—where temperatures are low enough for volatile compounds to condense').
To set off parenthetical or nonessential information, punctuation marks must be consistent on both sides.
2
Determine the matching punctuation mark needed to close the parenthetical element before the main clause begins.
Since the parenthetical phrase is opened with a dash, it must be closed with a dash to maintain consistency.
Mismatching a dash with a comma or parenthesis is grammatically incorrect in standard English conventions.

Key Concept

Dash pair consistency for nonessential parenthetical elements
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Topics

Dashes

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