单项选择题

A.COPY MODI1.TXT +MODI .TXT MODI3.TXT
B.COPY MODI1.TXT,MODI .TXT =MODI3.TXT
C.COPY MODI1.TXT +MODI .TXT =MODI3.TXT
D.COPY MODI .TXT +MODI1.TXT MODI3.TXT