等比数列{an}中,a1+a2=30,a3+a4=60,则a7+a8=( )(A)120 ... 问题详情:等比数列{an}中,a1+a2=30,a3+a4=60,则a7+a8=( )(A)120 (B)180 (C)240 (D)2...