下列符合可持续发展观念的是( )
A:封山育林
B:繁殖期禁止捕鱼
C:草场轮牧
D:围湖造田
如图甲所示,在匀强磁场中,一矩形金属线圈两次分别以不同的转速,绕与磁感线垂直的轴匀速转动,产生的交变电动势图象如图乙中曲线a、b所示,则( )
— Linda won first prize in the English speaking competition last week.
—Yes, she didn't let her teacher down.