Question 129·Hard·Boundaries
Researchers at the University of Lagos have designed a low-cost water purification _____ an innovation that, if widely adopted, could improve public health in underserved communities around the world, and are currently field-testing it in rural areas.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundaries questions, first decide whether the words after the blank form an independent clause or a nonessential insertion (like an appositive). Then choose punctuation that matches that structure: commas (or paired dashes/parentheses) for nonessential insertions, semicolons between two independent clauses, and colons only after an independent clause when introducing an explanation or list. Always check whether later punctuation in the sentence (like an existing comma) forces a matching opening mark at the blank.
Hints
Spot the interruption
Ask what the phrase starting with "an innovation" is doing: is it essential to identify the device, or is it extra information renaming it?
Look for a matching closing mark
Notice there is already a comma after "world". What punctuation would normally pair with that if the phrase is nonessential?
Check what comes after the inserted phrase
After the phrase, the sentence continues with ", and are currently...". Try reading each option aloud to see which one makes the full sentence grammatical.
Step-by-step Explanation
Identify the sentence structure
The main clause has the subject Researchers and a compound verb: they have designed a device and are currently field-testing it.
The words "an innovation that, if widely adopted, could improve..." rename the device, so they form a nonessential appositive inserted into the middle of the sentence.
Use the correct boundary punctuation for a nonessential appositive
A nonessential appositive inserted mid-sentence is typically set off by two commas:
- comma before the appositive begins
- comma after the appositive ends
In the text, there is already a comma after "world," which functions as the closing comma.
Eliminate punctuation that does not match the closing comma
- A semicolon must be followed by an independent clause; the following text is an appositive, not a new independent clause.
- A colon would make everything after it part of the colon construction; here that would create an ungrammatical structure (especially with the later ", and are currently...").
- An em dash used to set off an interruption mid-sentence should be paired with a second dash, not closed with a comma.
Select the option that correctly opens the appositive
Since the appositive is closed by the comma after "world," the blank should be filled with the opening comma: device,.
Therefore, the correct choice is device,.