Question 119·Medium·Boundaries
The satellite _____ reveal startling changes in the glacier's size.
Which choice completes the text so that it conforms to the conventions of Standard English?
When you see a descriptive phrase tucked between a subject and its verb, first remove the phrase to see if it’s nonessential. If it is, it must be set off with matching punctuation on both sides (typically commas); eliminate any choice with mismatched marks or with a semicolon/colon that would require a full independent clause after it.
Hints
Test whether the phrase is removable
Temporarily delete . If the sentence still works, the phrase is nonessential.
Use matching punctuation on both sides
Nonessential phrases need the same kind of boundary mark on the left and right.
Watch out for punctuation that requires two full sentences
A semicolon must separate two independent clauses; if what follows isn’t a full sentence, that choice can’t work.
Step-by-step Explanation
Identify the nonessential information
The phrase adds extra detail about the images but is not required for the sentence to make sense.
Apply the nonessential-phrase punctuation rule
A nonessential (parenthetical) phrase should be set off by matching punctuation on both sides, most commonly commas.
Check each choice for matching, standard punctuation
Read each option inserted into the sentence and verify that the punctuation on the left and right of the nonessential phrase is consistent and does not create a run-on or an incorrect break (like a semicolon before a dependent phrase).
Select the option that correctly sets off the phrase
The only choice that uses a comma before and after the nonessential phrase is images, taken over a five-year period,.