设S_k= $\frac{1}{k+2}$ + $\frac{1}{k+3}$ + $\frac{1}{k+4}$ +…+ $\frac{1}{2k-1}$ （k≥3，k∈N^*），则S_k+1=（   ）

根据短文内容理解，选择正确答案。    Hi, I'm Brian. This is the photo of my family. My grandfather is with glasses. He has little hair. The one standing next to him is my uncle. He is wearing a cap. My grandmother has gray hair. She is a kind woman. She is holding my younger brother. He has short curly hair. The woman standing behind me is my mom. She has straight brown hair. There is a little girl sitting on the table. Her name is Cathy. She is my sister. She is wearing a green T-shirt and a pair of green socks. It's her favorite color. Which one is my father? Well, he is wearing glasses, too. He is in brown shorts and brown shoes. His name is Sam. Now, do you know where he is?

下列句子中标点符号使用正确的一项是（    ）

已知如图，在直角坐标系xOy中，点A，点B坐标分别为（﹣1，0），（0， $\sqrt{3}$ ），连结AB，OD由△AOB绕O点顺时针旋转60°而得．

在公元前356年后的秦国，一个农民想获得爵位最好的办法就是去当兵，在战场上杀敌立功，这得益于（  ）