Geochemist Amara Velez, whose team studies mineral deposits in ancient caves, has developed a chronology of droughts in the Caribbean. _____ isotope patterns from formations in several caves rather than relying on the record from any one location, reduces the chance that a local disruption will be mistaken for evidence of a region-wide climate event.
Which choice completes the text so that it conforms to the conventions of Standard English?
For sentences with long modifiers, first strip away the descriptive material and identify the core subject-verb pair. Then determine whether the intervening words form a supplementary phrase; if they do, make sure matching punctuation sets off the phrase without separating the main subject from its verb.
Hints
Find the main verb
Look near the end of the sentence and identify the verb that agrees with the subject “method.”
Examine the middle phrase
Determine whether the text about isotope patterns makes the main assertion or merely describes how the method works.
Check the commas
The comma after “location” may be closing a supplementary phrase. Look for a choice that opens that phrase correctly.
Step-by-step Explanation
Identify the main clause
The main statement is “Velez's method reduces the chance.” Thus, “reduces” must remain the sentence's main verb.
Classify the intervening text
The words beginning with “comparing” describe how the method works. They form a supplementary participial phrase ending with the comma after “location.”
Complete the structure
A comma is needed after “method” to mark the beginning of that supplementary phrase: “Velez's method, comparing isotope patterns . . . , reduces the chance.”