已知等差数列{a_n}满足a₂=3，$S_n-S_{n-3}$=51(n>3) ， $S_n$= 100，则n的值为(   )

先通读下面的短文，掌握其大意，然后从A、B、C、D四个选项中选择可以填入空白处的最佳答案。

Dear Anna，

    How's your summer vacation going? I am having fun in Shanghai，China．I am sitting in a1now．It is big and there are about 50 tables in it．I am2some tofu and a small bowl of mutton noodles3carrots．I'm also drinking some red tea．I will450 yuan for the meal(餐)．The dumplings here look good ,and I will eat 5next time．

    The food here is very good. The noodles and the tofu are6, and the vegetables are fresh(新鲜的)，7the tea isn't very good．

    The people in the restaurant use chopsticks(筷子)to have meals．I8use them and I am learning9to use them．It is very interesting．I think it will take me a long time to10the meal．

    I will go back to New York next week．See you soon．

    Yours，

    Sally