题目

Before the college entrance examination, many students have shown________of tension. Some have trouble in sleeping while others have lost their appetite. A．anxiety           B．marks                C．signs              D．remarks 答案：C 解析: 略2．已知各项均为正数的数列{an}的前n项和为Sn，且2Sn=4an-1．在数列{bn}中，bn+1=bn-2，b4+b8=-16．（Ⅰ）求an，bn；（Ⅱ）设cn=$\frac{{b}_{n}}{{a}_{n}}$求数列{cn}的前项和Tn．