Question 204·Hard·Boundaries
Scientists have mapped only a fraction of the ocean _____ it difficult to predict how certain marine ecosystems will respond to climate change.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation and boundaries questions, first identify the structure on each side of the punctuation: decide whether each side is an independent clause, dependent clause, or phrase. Then match the punctuation to that structure: semicolons and periods for separating independent clauses, commas for attaching phrases or dependent clauses where appropriate. Always test the sentence for fragments or run-ons after inserting your choice, and be especially alert to -ing phrases at the end of a sentence, which are often nonessential participial phrases that should be set off with a comma.
Hints
Check if the second part is a full sentence
Look at the words after the blank: "making it difficult to predict how certain marine ecosystems will respond to climate change." Does this part have its own subject and verb, or is it just describing the situation from the first part?
Match punctuation to sentence structure
Remember that semicolons and periods usually separate two complete sentences. Ask yourself: if you put a semicolon or period in the blank, would the part starting with "making" be able to stand alone as a full sentence?
Think about -ing phrases at the end of sentences
When a sentence ends with a phrase starting with an -ing verb (like "making" or "causing") that adds extra information about the whole previous clause, how is that phrase usually punctuated?
Test the flow with and without a comma
Read the sentence out loud with no punctuation before "making" and then with a comma. Which version sounds like clear, standard written English?
Step-by-step Explanation
Identify the parts of the sentence
Read the full sentence with the blank filled in by each option:
"Scientists have mapped only a fraction of the ocean floor ____ making it difficult to predict how certain marine ecosystems will respond to climate change."
Notice that the first part (before the blank) is a complete sentence: it has a subject ("Scientists") and a verb phrase ("have mapped only a fraction of the ocean floor"). The part beginning with "making" explains a result or consequence of this action.
Decide what kind of phrase "making it difficult..." is
Look at the words after the blank: "making it difficult to predict how certain marine ecosystems will respond to climate change."
- This part begins with an -ing verb ("making") and does not have its own subject.
- That means it is not an independent clause (a complete sentence).
- Instead, it is a participial phrase that adds extra information about the main clause.
Eliminate punctuation that separates complete sentences
Because the "making" phrase is not an independent clause, it cannot stand alone as a sentence.
- A semicolon (;) and a period (.) are used to separate independent clauses.
- So any choice that uses a semicolon or period before "making" would incorrectly treat the second part as a full sentence.
This allows you to eliminate the options that create two separate sentences out of these parts.
Choose the correct way to attach the participial phrase
A participial phrase that gives extra information about the entire previous clause is usually set off by a comma, not fused directly into the sentence and not separated as its own sentence.
The only option that correctly attaches the participial phrase to the main clause with a comma is:
D) floor, making.