第19题:[不定项选择题]Man can eventually land on Venus only when A.the algae have done their work B.the atmosphere becomes cooler C.there is oxygen D.it rains there 参考答案:D 由最后一段中“before man can set foot on Venus it will be necessary for the oxygen to pro.duce rain”可知,只有金星上有降雨,人类才最终有可能在上面着陆。所以正确答案为D。
第20题: [多项选择]下列属于消防防坠落辅助设备的有() A. 腰斧 B. 安全钩 C. 上升器 D. 八字环 参考答案:B, C, D