A:y1>y2>0
B:y1<y2<0
C:y2>y1>0
D:y2<y1<0
已知数列{an}的前n项和为Sn,满足Sn+1=2Sn+2n+1(n∈N*),且a1=1.
(Ⅰ)求证{an+2}是等比数列;
(Ⅱ)求Sn.
地球上最大的生态系统是____.