— Who is singing in the next room?
— It be Lucy. She likes singing at this time.
“葵花朵朵向太阳”所表现的生物特征是( )
真空中相距为3a的两个点电荷M、N,分别固定于x轴上x1=0和x2=3a的两点上,在它们连线上各点场强E随x变化关系如图所示,以下判断正确的是( )