有一学生成绩管理数据库如下表，要求建立一SAS数据集score，并输出显示 创建一个新的数据集class，新增平均成绩aver变量和等级考评grade变量，grade的值是根据aver值的大小给出A、B、C、D四个等级，并显示新数据集cla-A student achievement management database as the table, called for the establishment of a SAS data set score, and output display　create a new data set class, add an average score aver evaluation variables and grade level variables, grade values are based on the size of a aver value the A, B, C, D four grades, and displays the new data set of class