A. ff he lets dead leaves decay in the soil by themselves B. if he makes the humus decrease after taking away his crops C. by clearing away all the dead leaves D. by burning waste plant material lying about 参考答案:B 答案解析:根据第一段中的“He grows a crop and takes it away to eat;then there ale no dead leaves to fall on the ground
第6题: [单项选择]提高模具的硬度、耐磨性可采用()工艺 A. 采用合金钢 B. 淬火+低温回火 C. 合理设计模具 D. 调质 参考答案:B
第7题: [单项选择]枪:子弹 A. 汽车:汽油 B. 门:窗户 C. 桌子:椅子 D. 表带:手表 参考答案:A 答案解析:枪一定需要子弹才能发射使用,汽车一定需要汽油才能驾驶使用,故选A。