区分蚯蚓的前端与后端,通常依据( )
A:口的位置
B:体节的大小
C:环带的位置
D:肛门
如图所示,有一束光斜射入盛水的容器中,在容器底形成一个光斑,保持入射光路不变,慢慢放出容器中的水,则容器底的光斑将( )
Meyer and his team were the first ______ how the disease spreads from animals to humans.