(单选题, )下面代码：A = input("").split(",")If isinstance(a,list): print("{} is list".format(a))Else: print("{} is not list".format(a))代码执行时，从键盘获得1,2,3，则代码的输出结果是（ ）
A.执行代码出错
B.1,2,3 is not list
C.['1', '2', '3'] is list
D.1,2,3 is list
正确答案是C