A punctuation question tests how a relative clause, a group of words that describes a noun, joins a sentence. Read around the blank, then find the main subject and verb and check whether each part can stand alone. A semicolon joins two complete sentences; a colon follows a complete sentence and introduces a list or explanation. Use commas for details that aren't needed to identify a noun, and no commas for details that are. Check what the mark would separate when a relative clause follows a noun.
Hints
- Hint 1
Start with “Her work” and find its main verb. Set aside the words describing the Dover House while you do.
- Hint 2
Ask what the ending about inspiring engineers does: does it give a separate sentence, or add a detail to something already mentioned?
Step-by-step
Separate the main sentence from the added detail
Step 1Find the complete main sentence
Her work on the Dover House is the subject, so ask what that work did. The description of the home delays the answer, but we reach the main verb in demonstrated the practicality of solar thermal storage. With systems added after storage, her work demonstrated that those systems were practical. We're choosing punctuation to join the ending to a complete main sentence.
- Step 2
Test whether the ending stands alone
Can inspired later generations of engineers start a new sentence when which comes first? No: which links it to systems, so it's a dependent clause, a group of words that can't stand alone as a sentence. The ending describes earlier words, which rules out the version with a semicolon because a semicolon needs a full sentence after it. A colon can introduce an explanation or list after a full sentence. It can't separate systems from the added which clause that describes them, so the version with a colon also fails.
- Step 3
Mark the start of the extra information
What punctuation does an added which clause need? A comma goes before which, so the version with no mark leaves out the opening comma. The detail inspired later generations of engineers runs to the sentence’s end, so the period closes it without a second comma. systems, which adds that opening comma and keeps the detail attached to the main sentence. Choice B.