单选题

以下程序段运行后,输入:ABCdef,输出应为(    )

char ch;
while ((ch = getchar ()) != '\n')
{
   	if (ch >= 'A' && ch <= 'Z')
      	ch = ch + 32;
  	else if (ch >= 'a' && ch <= 'z')
      	ch = ch - 32;
  	cout << ch;
}
A

ABCdef

B

abcdef

C

ABCDEF

D

abcDEF

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