A.an+1≥bn+1 B.an+1＜bn+1 C.an+1=bn+1 D.an+1＞bn+1
A.an+1≥bn+1 B.an+1＜bn+1 C.an+1=bn+1 D.an+1＞bn+1
思路解析：利用数列的知识在求出an+1的关系式时考虑用到均值定理得出与bn+1的关系式.
{an}的公差为d，{bn}的公比为q，a1=a=b1，a2n+1=a1+2nd，b2n+1=aq2n，又a+2nd=a·q2n，∴nd=
(q2n-1).∴an+1=a+
(q2n-1)= 
(q2n+1)≥
·2·
=a·qn=bn+1.因此，选A.其他选项当然都不正确.
答案：A