Question 78·Hard·Boundaries
Growing evidence from satellite images indicates that the Amazon rainforest is approaching a tipping point beyond which tree loss could accelerate _____ scenario that climatologists warn about as one that would irreversibly alter regional weather patterns.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundary questions, decide whether the words after the blank form an independent clause. If they do, a period or semicolon may work; if they don’t (for example, they form an appositive noun phrase), you generally need a comma (or sometimes a dash) to attach them to the main clause.
Hints
Check what comes after the blank
Look at what follows the blank: “scenario that climatologists warn about as one that would irreversibly alter regional weather patterns.” Does that part have a main verb that would make it a complete sentence by itself?
Decide whether the second part is a renaming/explanation
Ask whether the words after the blank are naming/explaining the whole idea before the blank (an appositive noun phrase). If so, you typically attach it with a comma.
Test semicolon/period rules
A semicolon or a period should separate two complete sentences. Read what would come after the semicolon/period as its own sentence and check whether it’s truly a complete independent clause.
Step-by-step Explanation
Locate what comes before and after the blank
Read the sentence with the blank:
“Growing evidence from satellite images indicates that the Amazon rainforest is approaching a tipping point beyond which tree loss could accelerate _____ scenario that climatologists warn about as one that would irreversibly alter regional weather patterns.”
The blank comes right after the verb phrase “could accelerate,” and it must supply “rapidly” plus any needed punctuation to connect what follows.
Identify the function of the words after the blank
The words after the blank begin with:
“a scenario that climatologists warn about as one that would irreversibly alter regional weather patterns.”
This is a noun phrase describing/renaming the situation just mentioned (tree loss accelerating rapidly). It is not set up as a complete independent clause that can stand alone.
Choose punctuation that matches the grammar
Because the phrase after the blank is an appositive noun phrase, it should be attached to the prior clause with a comma.
- A semicolon and a period are used to separate independent clauses, which is not what follows the blank here.
- No punctuation creates an ungrammatical run of words.
Eliminate the incorrect choices and select the best one
Check each option in context:
- “rapidly; a”: a semicolon incorrectly separates the clause from a noun phrase.
- “rapidly a”: missing punctuation before an appositive noun phrase.
- “rapidly. A”: creates a sentence fragment by making the noun phrase stand alone.
Only “rapidly, a” correctly joins the clause to the appositive noun phrase. So the correct answer is “rapidly, a”.