能源、信息、材料是现代社会发展的三大支柱,下列说法正确的是( )
一I think I've got a bad cold,Doctor.Shall I take some medicine?
一No need.Your body itself is able to the virus. Just drink more water and rest.
如图表示春季某蔬菜大棚内一昼夜CO2浓度的变化曲线,假设6时日出、18时日落.请回答下列问题:
-13的绝对值是………………………( )