“锄禾日当午”中的“锄禾”即为疏松土壤，其生物学的意义是（　　）

下列属于不良学习习惯的是（  ）

电阻R₁、R₂串联接在电路中，R₁两端的电压为3伏，R₂两端的电压为9伏，R₁+R₂=600欧，求：

从物理学的角度对一下成语进行解释，正确的是（  ）

      On weekdays, David gets up at 6:30.He has breakfast at seven and then he goes to school by bus. He gets there at 7:15. He doesn't like to be late. Classes begin at 8:00. He has lunch at twelve at school. He goes home at 5:30 in the afternoon. On weekends, he gets up at about 8:00 and makes breakfast for his family. His parents like him very much.