Marine fossils have been discovered at elevations exceeding 26,000 feet in the _____ fossils could have formed only in marine environments, their presence supports the conclusion that tectonic forces later lifted the fossil-bearing rocks far above sea level.
Which choice completes the text so that it conforms to the conventions of Standard English?
In challenging boundaries questions, identify every clause in the full sentence rather than checking only the punctuation nearest the blank. A choice that appears to fix the first boundary may leave a later comma splice; determine whether conjunctions make clauses independent or dependent before selecting the punctuation.
Hints
Locate every clause
Identify each subject-verb pair, and determine which clauses can stand alone as sentences.
Check the entire completion
Do not evaluate only the boundary after “Himalayas.” Also inspect the comma after “marine environments.”
Consider subordination
Ask whether the inserted wording can make the clause before the later comma dependent, allowing the clause after that comma to serve as the main clause.
Step-by-step Explanation
Identify the clauses
The text contains three subject-verb units: “Marine fossils have been discovered,” “those fossils could have formed,” and “their presence supports.” The first and third are independent clauses.
Inspect the later comma
If “those fossils could have formed only in marine environments” remains an independent clause, the comma after “environments” incorrectly joins it to the independent clause beginning with “their presence.” Therefore, merely placing a period or semicolon after “Himalayas” does not repair the entire sentence.
Create the correct sentence structure
A period correctly ends the first independent clause after “Himalayas.” The subordinating conjunction “Because” then makes “Because those fossils could have formed only in marine environments” a dependent introductory clause, which can correctly be followed by a comma and the main clause beginning with “their presence.”