题目

等差数列中，已知，，则的前项和的最小值为（    ） A．              B．              C．              D． 答案：．C 【详解】∵等差数列中，，∴，即.又，∴的前项和的最小值为.故答案选C The entry point tissue in the very front of eye functions as the window ______ all light has to pass on its way. A. which                       B. that                             C. across which         D. through which