【正确答案】 B

【答案解析】本题问根据Dr. Weiss所说，第二干冷期所产生的影响是什么。第三段中“...Dr. Weiss observes that the development of irrigation coincides with a second cool，dry period...Farmers would thus have been forced out of the area in search of other opportunities．”Dr. Weiss认为干冷期将会迫使农民背井离乡寻求别的生计。第四段中紧接上段“Once again，an innovative spark was required...．some of these displaced farmers that the slow-moving waters...could be diverted using cabals...”表明农民在走投无路的时候想到了使用沟渠引水灌溉的办法，于是发明了灌溉。所以[B]“促进了沟渠的利用”正确。 [A]改变了生长季节：第三段中"His analysis...suggests that rainfall...would...have fallen below the level needed to sustain fanning reliably．"表明干冷期的降水量无法保证耕种正常进行。但这并不表明生长季节发生了变化。 [C]迫使农民放弃了农业：文中提到“Farmers would thus have been forced out of the area in search of other opportunities．”。接着又提到农民在走投无路的时候想到了利用沟渠引水灌溉的办法。也就是说，由于发明了灌溉，农民们并没有放弃农业。 [D]导致人口减少：第三段中“Farmers would thus have been forced out of the area”及第四段中“some of these displaced farmers”都表明农民是被迫迁移，而没有谈到人口数量减少。当然，由于气候对农业的影响，人口很可能减少，但是在本文中没有谈到这点，因此不能选本项。本项只是出题者根据常识而设置的干扰项。