A punctuation question tests where a sentence's parts need to be separated. Read across the blank and ask which parts can stand alone. A semicolon joins two complete sentences, while a comma can attach extra information that can't stand alone. Cross out possible extra information to check that the main sentence still works, but leave words needed to finish its thought attached. Check punctuation around the linking word separately: commas set off an interruption, not a word that directly describes the verb that follows.
Hints
- Hint 1
Start with the thought before the blank. Once you add the noun after fossil, does that thought need the database detail to make a complete sentence?
- Hint 2
Cross out the words from generating to the end. What remains, and could the removed words stand alone as a new sentence?
- Hint 3
Check what thereby describes. Does it describe generating directly, or add a separate side comment?
Step-by-step
Test the ending and the linking word
Step 1Find where the main sentence is complete
The researchers analyzed tells us who did what, but analyzed still needs us to say what they studied. For this punctuation question, we need to find where that thought becomes complete. What did the researchers analyze? Over 2,000 fossil specimens, so the main sentence is complete at specimens and the database detail comes after a full sentence.
- Step 2
Test whether the ending can stand alone
Can generating a database stand alone as a second sentence? Generating only describes the result here; a new sentence would need someone doing the generating and a verb such as generated. The words that has become a crucial reference for paleontologists worldwide describe the database, so has become doesn't make the whole ending a full sentence. Cross out the database detail, and the researchers' sentence still works, showing that the ending adds extra information to a complete sentence.
- Step 3
Find what the linking word describes
What role does thereby play beside generating a database? It means by doing that, so the researchers generated the database by analyzing the fossils. Thereby directly describes generating, rather than interrupting the phrase with a side comment. A word can be removable and still belong directly with a verb, so we don't automatically put commas around it.
- Step 4
Attach the ending with one comma
The added result needs one opening comma, because the sentence's end closes it. Put that comma after specimens, before the result phrase that runs through paleontologists worldwide. Leaving thereby directly beside generating gives us specimens, thereby. Choice B.