搜题请搜索小程序“爱下问搜题”
问题 选择题

等差数列{an}的公差不为零，首项a1=1，a2是a1和a5的等比中项，则数列{an}的前10项之和是（　　）

A．90

B．100

C．145

D．190

答案

．由题意知，（a1+d）2=a1（a1+4d），

即a12+2a1d+d2=a12+4a1d，

∴d=2a1=2．

∴S10=10a1+

10×9
2
d=10+90=100．

故选B

写作题

你收到一封咨询信，请你以旅行社工作人员的身份完成任务。

Dear Ace Travel,

     I'm Li Ming, from the east of China. For the coming winter vacation, my family and I want to spend our

vacation in a foreign city for ten days. We would like to go somewhere not only warm but also interesting.

We don't mind how far we have to go. It has to be a place where we can swim everyday, and it would be

nice if our hotel is not expensive but clean and comfortable. We like to pay no more than $ 5,000 for the

trip. Could you please give us your suggestions for vacation spots?

Thanks a lot. 

                                                                                                                                              Yours, 

                                                                                                                                              Li Ming

      请你根据来信，从下列所给的地方中选择一个或两个符合Li Ming要求的地方，向他提出建议。

（80字左右）

Tokyo, Sydney, Hawaii, Shanghai

                                                                                                                                                        

                                                                                                                                                        

                                                                                                                                                        

查看答案
单项选择题 A1/A2型题

感应神经性耳聋的听力学特点是（）。

A.Rinne试验AC

B.气骨导差小于20dB

C.Weber试验偏向健侧

D.镫骨肌反射不存在

E.中度以下听力损失DPOAE消失
查看答案