A:①②④
B:①②③
C:②③④
D:①③④
—What's your new home like?
—_______________________.
在数列{an}中,若a1=2,an+1=(﹣1)n(an﹣1),则a5=____
____,壮士一去兮不复还。(《荆轲刺秦王》)