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Question

Difficulty: EasyDashes

Dorothy Hodgkin, a pioneer in X-ray crystallography, determined the structures of important biochemical substances. Her most famous breakthrough—the structure of penicillin, was resolved in 1945 after years of meticulous analysis.

Which of the following options is the best alternative to the underlined portion of the sentence?

  1. A
    breakthrough—the structure of penicillin, was
  2. breakthrough—the structure of penicillin—wasAnswer
  3. C
    breakthrough; the structure of penicillin, was
  4. D
    breakthrough, the structure of penicillin; was

Answer

breakthrough—the structure of penicillin—was
The correct answer properly utilizes matching em dashes to enclose the non-essential appositive phrase 'the structure of penicillin'. In standardized English grammar, non-essential elements must be set off with identical punctuation marks on both sides. Since an em dash is used to open the phrase, a second em dash must close it before the sentence's main verb.

Step-by-Step Solution

1
Identify the non-essential phrase in the sentence that provides additional, parenthetical information.
The phrase 'the structure of penicillin' is a non-essential appositive that clarifies what the 'most famous breakthrough' refers to.
Identifying the non-essential phrase helps determine that it must be set off from the rest of the sentence using consistent punctuation marks at both its start and end.
2
Evaluate the punctuation surrounding the non-essential phrase to ensure consistency.
An em dash is used immediately before the phrase. To maintain punctuation consistency, a matching em dash must be used immediately after the phrase before the main verb.
ACT grammar rules state that parenthetical elements must be enclosed by matching punctuation marks: either two commas, two parentheses, or two em dashes. Mixing an em dash with a comma is incorrect.

Key Concept

Using matching pairs of dashes to set off non-essential parenthetical information.
Estimated Time:45s
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