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...
He phoned on Tuesday, just before you came...他星期二来电话了，就在你来之前。Mary phoned that her son was lost.玛丽打电话来说她儿子失踪了。I phoned twice a day, leaving messages with his wife...我每天打两次电话，托他妻子捎口信。Mr Patel phoned the University for an e...