①延缓人口老龄化的进程 ②改变我国人口负增长现状
③有利于提高人口素质 ④保持合理的劳动力数量
A:①②
B:②④
C:②③
D:①④
—Nero is crying. Do you know _______ she's so upset?
—Well, she lost her pet cat which was just like her family member.
f(x)在x0处可导,a为常数,则lim△x→∞fx0+a△x-fx0-a△x△x=( )
Li Yang, the founder of Crazy English, says that he copies it down________he comes to a beautiful sentence.