A:a2
B:a4
C:a6
D:a8
-- It's snowing. I really want to run outside and make a snowman.
-- Why not have a snow ball fight instead? It's more exciting.
如图为某生态系统的食物网示意图,请根据图回答下列问题
某发光点S发出的两条光线经平面镜反射后分别沿O1A和O2B方向射出,根据平面镜成像规律,请在图中画出发光点S的位置.
为了探究浮力大小与液体密度的关系,老师准备了如图所示的器材供同学们选择,同学所选的四组器材中,能达到探究目的是(不能多选或少选器材)( )