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Difficulty: MediumCommas with Lists, Clauses, and Coordinate Adjectives

While studying historical climate patterns, dendrochronologists collected core samples from ancient bristlecone pines, they measured the ring widths with microscopes, and cross-dated the growth patterns against established regional master chronologies.

Which choice provides the correct punctuation and grammatical structure for the underlined portion?

  1. A
    NO CHANGE
  2. B
    pines; measured the ring widths with microscopes, and cross-dated
  3. pines, measured the ring widths with microscopes, and cross-datedAnswer
  4. D
    pines, measured the ring widths with microscopes and cross-dated,

Answer

pines, measured the ring widths with microscopes, and cross-dated
The correct phrasing creates a parallel list of three verb phrases ('collected core samples...', 'measured the ring widths...', and 'cross-dated the growth patterns...') that all share the subject 'dendrochronologists'. Commas are correctly used to separate each item in the three-part series, including the serial comma before the coordinating conjunction 'and'.

Step-by-Step Solution

1
Identify the grammatical structure of the sentence
The sentence consists of a single subject ('dendrochronologists') performing three sequential actions in a list format.
Recognizing that the actions form a series of parallel verb phrases dictates the appropriate punctuation rules.
2
Analyze parallel verb series punctuation
Three items in a series require commas separating each item: item 1 ('collected...'), item 2 ('measured...'), and item 3 ('cross-dated...').
Items in a list must maintain parallel construction without introducing unnecessary pronouns or semicolons.
3
Select the option with clean list separation and correct comma placement
The phrase 'pines, measured the ring widths with microscopes, and cross-dated' correctly maintains parallelism and proper list commas.
This choice avoids creating a comma splice or splitting the verb from its direct object.

Key Concept

Commas with parallel items in a series
Estimated Time:45s
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Topics

Commas with Lists, Clauses, and Coordinate Adjectives

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