Visual Basic程序问题
与程序段：
a = a + b
b = a - b
a = a - b
功能相同的程序段是
A．a = b
b = a
B．a = a + b
a = a - b
b = a - b
C．t = a
a = b
b = t
D．If a > b Then
a = b
Else
b = a
End If
答案是C,为什么呢?