OG详解-OG7 文法 Q3

Choice D is the best answer. The convention being tested is the use of verbs to express tense in a sentence. In this choice, the past tense verb “affected,” used in conjunction with the phrase “during this time,” correctly indicates that the dust storms occurred in the 1930s. 
Choice A is incorrect because the present progressive tense verb “are affecting” doesn’t indicate that the dust storms occurred in the 1930s. Choice B is incorrect because the future perfect tense verb “will have affected” doesn’t indicate that the dust storms occurred in the 1930s. Choice C is incorrect because the future tense verb “will affect” doesn’t indicate that the dust storms occurred in the 1930s.