题目

Although he is considered a great writer，_____．（ ） A．his works is not widely read B．but his works are not widely read C．however his works are not widely read D．yet his works are not widely read 答案：D用油膜法估测油酸分子的大小，实验器材有：体积分数(含油酸体积与油酸酒精溶液总体积比)为c的油酸酒精溶液、最小刻度为0．1mL的量筒，盛有适量清水的45×50cm的浅盘．痱子粉、橡皮头滴管、玻璃板、彩笔、坐标纸．(1) 下面是主要实验步骤．请补全所缺步骤a．用滴管将体积分数为c的油酸酒精溶液一滴一滴的滴入量筒中，记下滴入油酸酒精溶液的体积为V时的滴数N；b．将痱子粉均匀撒在浅盘内的水面上，用滴管吸取体积分数为c的油酸酒精溶液，从低处向水面中央一滴一滴的滴入，直到稳定的油酸薄膜有足够大的面积而又不与器壁接触时为止，记下滴入的滴数n；c                                                                      ;d. 将画有油酸薄膜的玻璃板放在坐标纸上计算轮廓内正方形的个数，算出油酸薄膜的面积S．(2) 用已知量和测得量表示单个油酸分子的直径为                  .