A:金丝雀虉草的胚芽鞘中生长素的极性运输
B:缩手反射时兴奋在神经元间的传递
C:人体血浆和组织液间的物质转移
D:草原生态系统中狼和兔子间的能量流动
—We should go to school by bus instead of by car.
—Yeah, cars we use, pollution there will be.
小磁针静止在如图所示的位置,请你在图中标出小磁针的N极和S极。