办公自动化(OA)是目前广泛开展的一项计算机应用。按分类，它应属于下列( )类应用。

A．DSEG SEGMENT
WDAT EQU WORD PTR BDAT
BDAT DB 12H，34H
DSEG ENDS
B．DSEG SEGMENT
BDAT DB 12H，34H
WDAT = WORD PTR BDAT
DSEG ENDS
C．DSEG SEGMENT
WDAT EQU THISWORD
BDAT DB 12H，34H
DSEG ENDS
D．DSEG SEGMENT
BDAT DB 12H，34H
WDAT LABEL WORD
DSEG ENDS

A．PUSH SI
PUSH DI
POP SI
POP DI
B．PUSH SI
PUSH DI
POP DI
POP SI
C．MOV AX，SI
MOV SI，AX
MOV DI，BX
D．MOVAX，SI
MOV BX，DI
XCHG BX，AX