以下程序的输出结果是： fo = open("text.txt",'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
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