(单选题, )以下程序的输出结果是（ ）
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()
Fo = open("text.csv",'r')
Print(fo.read())
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
正确答案是D