A.sometimesB.oftenC.usuallyD.seldom
A. sometimes
B. often
C. usually
D. seldom
A.supplyB.findC.100k forD.give
A. supply
B. find
C. 100k for
D. give
A.atB.toC.towardsD.on
A. at
B. to
C. towards
D. on
已知数列{an}的前n项和为Sn,且S2n-1=4n2-2n+1,则Sn等于() (A)n2+n (B)n2+n+1 (C)4n2+l (D)4n2-2n