Which choice completes the text so that it conforms to the conventions of Standard English?
A
occurs
B
have occurred
C
occur
D
are occurring
Explanation
Correct answer: A.
Choice A is the best answer. The convention being tested is subject-verb agreement. The singular verb "occurs" agrees in number with the singular subject "radiation."
Why the other choices are wrong
Choice B
Choice B is incorrect because the plural verb "have occurred" doesn’t agree in number with the singular subject "radiation."
Choice C
Choice C is incorrect because the plural verb "occur" doesn’t agree in number with the singular subject "radiation."
Choice D
Choice D is incorrect because the plural verb "are occurring" doesn’t agree in number with the singular subject "radiation."