A:①③
B:①②
C:②③
D:③④
每一种鸟的生殖和发育过程都必须经历的是( )
若fx为偶函数,且当x≥0时,fx=x3π-cosx,则fx的零点个数为 ( )
Li Ming used on the right in China, but he soon got used on the left in England.