The radiation that ______ during the decay of radioactive atomic nuclei is known as gamma radiation.
occurs
have occurred
occur
are occurring
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."
Choice B is incorrect because the plural verb "have occurred" doesn’t agree in number with the singular subject "radiation."
Choice C is incorrect because the plural verb "occur" doesn’t agree in number with the singular subject "radiation." Choice D
is incorrect because the plural verb "are occurring" doesn’t agree in number with the singular subject "radiation."