OG3 阅读 Q49

Choice A is the best answer. In (lines 43-45"where... source"), the authors propose a scien-tific trial in which honeybees are "offered a number of pyrethrum producing plants, as well as a typical bee food source such as clover." Since the authors contrast the "pyrethrum producing plants" with clover, a "typical bee food source," it can be assumed that clover does not produce pyrethrums.
Choice B is incorrect because it is stated in the passage. Choices C and D are incorrect because they are not assumptions made by the authors.