A:contribute to
B:appeal to
C:attend to
D:devote to
______ I am not rich, ______ I still feel very happy.
美丽的蝴蝶是由“毛毛虫”变成的,在昆虫的生殖和发育过程中,“毛毛虫”是( )
若a+b<0,ab>0,则P(-a,b)所在的象限为( )