单项选择题
In the following statements about functional dependency, which one is incorrect ( )
A．if X’
X, then X→X'
B．if X→Y and Y’
Y, then X→Y'
C．if X→Y and X’
X, then X'→Y
D．if X→Y and Y→Z, then X→Z
X, then X→X'B．if X→Y and Y’
Y, then X→Y'C．if X→Y and X’
X, then X'→YD．if X→Y and Y→Z, then X→Z