题目

设数列{an}的前n项和为Sn(n∈N*),关于数列{an}有下列三个命题: ①若{an}既是等差数列又是等比数列,则an＝a n+1(n∈N*); ②若Sn＝an2+bn(a,b∈R),则{an}为等差数列; ③若Sn＝1-(-1)n,则{an}是等比数列. 这些命题中正确命题的序号是__________. 答案：①②③语法填空（共10小题；每小题1.5分， 满分15分） 阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将答案填写在答题卡标号为16-25的相应位置上。   Making new friends means __1.______（put） yourself out on a limb and asking others not only to accept you, but to like you and want to be around you as well. ____2.__(fortunate)， there is no magical solution ____3.____ this part of the process, so if you want to make friends, take a deep breath and jump right in!   4.__ first step to making new friends is figuring out what is holding you back. A lot of times people 5.____ are interested in making new friends don’t know why they don’t have them already. They can’t see that _6.___ own actions are working against them.   Once you can identify(确认，确定) what is keeping you from making new friends, you need to work through these concerns. This can be painful _7.___ you will need to put yourself outside of your comfort zones to see any real differences.   The next step is to shine in these social settings so that others will leave with a positive ___8.___ (impress). If you find social situations hard, just rely on a few simple rules.   When you feel ___9.___ (confidence) that you’ve made some great new friends, get out there and celebrate with them! No matter ____10.____ you decide to do, the important thing is to celebrate your new friends and hopefully continue cultivating more.