Which choice completes the text so that it conforms to the conventions of Standard English?
A
do they affect our weather.
B
they do affect our weather.
C
do they affect our weather?
D
they do affect our weather?
Explanation
Correct answer: C.
Choice C is the best answer. The convention being tested is end-of-sentence punctuation. This choice correctly uses a question mark to punctuate the coordinated interrogative clauses "What are atmospheric rivers" and "how do they affect our weather," both of which ask direct questions.
Why the other choices are wrong
Choice A
Choice A is incorrect because a period can’t be used in this way to punctuate an interrogative clause, such as "how do they affect our weather," at the end of a sentence.
Choice B
Choice B is incorrect because the structure requires an interrogative clause and a question mark at the end of the sentence.
Choice D
Choice D is incorrect because the structure requires an interrogative clause at the end of the sentence.