如果从键盘上输入:ABCdef,则下面程序段的输出结果是( )。char ch;while((ch=getchar())!='\n'){
     if(ch>='A' && ch<='Z') ch=ch+32;     else if(ch>='a' && ch<='z') ch=ch-32;     printf("%c",ch);}printf("\n"); A.

ABCdef B.

abcDEF C.

abc D.

DEF