菜青虫喜食油菜叶,同一菜田中的菠菜上却难觅菜青虫踪迹,菜青虫这一行为属于( )
A:学习行为
B:先天性行为
C:社会行为
D:迁徙行为
Tom likes playing _____volleyball, and his sister likes playing______ piano.
世界上高原面积广大,有“高原大陆”之称的大洲是( )