以下程序的输出结果是(向文件中写入的结果)：（ ）。fo = open("text.csv",'w')x =[[90,87,93],[87,90,89],[78,98,97]]b = []for a in x:for aa in a:b.append(str(aa))fo.write(",".join(b))fo.close()

A. [90,87,93,87,90,89,78,98,97]
B. 90,87,93 87,90,89 78,98,97
C. [[90,87,93], [87,90,89], [78,98,97]]
D. 90,87,93,87,90,89,78,98,97