为保持土壤肥力,农民搞作物轮作.Farmers rotate their crops so that the soil will remain fertile.农作物轮作有助于防止水土流失.Crop rotation helps prevent soil erosion.他连续5年在同一块地里种植不同的作物，研究人员称之为轮作。He grew a different crop on the same field five years i...
Their morale was low because they did not want to march in parades every Sunday afternoon.他们士气低落,因为他们不愿意每个星期日下午都列队操练.He always parades his superiority and strives to outshine others.他总是逞强好胜.Don't rain on other peopl...
碳、氢、氧化合形成碳水化合物和脂肪。Carbon, hydrogen and oxygen combine chemically to form carbohydrates and fats.5月份工程师们在一条氢燃料管线上发现一条裂隙。In May engineers found a leak in a hydrogen fuel line.氢与氧化合成水。Hydrogen and oxygen combine to form wat...