第18题: [单项选择]An ignorant farmer will make the land poorer______. 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