A punctuation question tests how marks and connecting words separate or connect sentence parts. Start by reading the whole sentence, including punctuation that stays the same. Then test each join: which parts can stand alone, and which depend on another part? A period separates full sentences, a semicolon connects them, and a comma alone can't connect them. A comma can follow an opening part that can't stand alone, and connecting words can change whether a part stands alone.
Hints
- Hint 1
Read from the blank to the end, paying attention to the comma after the part about marine environments.
- Hint 2
Test whether each part around that comma can stand alone. Look for who or what each part is about and the verb that goes with it.
- Hint 3
A comma can attach a part that leans on another part, but it can't join two full sentences by itself. Check both joins using the completed wording.
Step-by-step
Test both sentence joins
Step 1Check beyond the changed mark
Compare Himalayas. Those with Himalayas; those. A period can separate full sentences that stand alone, and a semicolon can connect them. Does that make either version work all the way to the end? Every join must work, so let's test the comma in marine environments, their presence supports.
- Step 2
Test the comma farther along
What does the later comma join? In fossils could have formed only in marine environments, fossils is the subject, the thing the words are about. The main verb, could have formed, says what those fossils could have done. their presence supports the conclusion also stands alone: presence is the subject, and supports is the verb. A comma alone between these full sentences makes a comma splice, an incorrect join.
- Step 3
Test the join at the blank
Before the blank, Marine fossils have been discovered also has a subject and main verb, and the location completes the thought. What happens with Himalayas, those? It joins that full sentence to the one about where fossils formed with only a comma, adding another comma splice.
- Step 4
Attach the opening reason
How can the later comma work? Himalayas. Because those ends the first full sentence with a period, then changes the next part. Because makes the part about marine environments depend on what follows: because the fossils formed at sea, what does their presence show? The words their presence supports the conclusion answer that question, so the comma attaches the opening reason to a full sentence. Choice D.