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Question

Difficulty: EasyCommas with Nonessential and Parenthetical Elements

In 1928, Scottish biologist Alexander Fleming made an accidental discovery in his laboratory. A strange mold, which grew in a neglected petri dish, was killing the surrounding bacteria. This chance observation led to the development of penicillin, the world's first modern antibiotic.

Which choice best punctuates the underlined portion of the sentence?

  1. NO CHANGEAnswer
  2. B
    mold, which grew in a neglected petri dish
  3. C
    mold, that grew in a neglected petri dish,
  4. D
    mold; which grew in a neglected petri dish,

Answer

NO CHANGE
The correct choice is the original phrasing because the relative clause 'which grew in a neglected petri dish' is nonessential and is properly set off with a pair of commas: one before the clause starts and one after it ends.

Step-by-Step Solution

1
Determine if the relative clause 'which grew in a neglected petri dish' is essential (restrictive) or nonessential (nonrestrictive) to the basic meaning of the sentence.
The clause is nonessential because 'a strange mold' is already identified, and removing the clause does not alter the main point of the sentence.
Nonessential information must be set off from the rest of the sentence with punctuation, while essential information should not be set off.
2
Select the correct punctuation to set off the nonessential relative clause.
A matching pair of commas must be used, with one comma immediately before the clause and one comma immediately after it.
Omitting one of the commas, using a semicolon, or placing commas around a restrictive clause violates standard punctuation conventions.

Key Concept

Commas with Nonessential and Parenthetical Elements
Estimated Time:45s
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Topics

Commas with Nonessential and Parenthetical Elements

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