Explanation

The passage explains how the damage caused by repeated invasions of locusts in the nineteenth century caused farmers west of the Mississippi River to diversify. Since wheat, the dominant crop in the region, was especially susceptible to damage from locusts, it made sense for farmers to lower their wheat production and raise their production of other crops and animals less vulnerable to locust invasions.

Question 19

Choices A and C are correct.

Choice A is correct: according to the passage, “wheat had come to nearly monopolize the region” prior to the recommendations of government entomologists.

Choice B is incorrect: although wheat was the dominant crop, there is no indication that peas and beans had not been planted in the region prior to the admonishments of government entomologists.

Choice C is correct: given that wheat was the dominant crop, only a relatively small portion of farmland could have been devoted to other crops.

Question 20

In discussing the advantages of less vulnerable crops, the author describes corn as “robust.” Of the choices presented, “vigorous” is most similar in meaning to “robust.” Neither “crude” nor “demanding” is an advantage, and although being “productive” or “rich” might be desirable, neither matches the meaning of “robust” in this context. Therefore, Choice D is the correct answer.