By analyzing soil samples, geologists can determine the age of ancient _________ layers reach back millions of years.
4
writingWhich choice completes the text so that it conforms to the conventions of Standard English?
A
rock until
B
rock; until
C
rock: until
D
rock, until
Correct Answer: D
Choice D is the best answer. A comma is used to separate the independent clause "geologists can determine..." from the dependent clause starting with "until."
Choice A is incorrect because it creates a run-on. Choice B is incorrect because a semicolon separates independent clauses, but the second clause is dependent. Choice C is incorrect because a colon is inappropriate here.