[单选题]
Which of the below is a characteristic prw)urgzq2sop *+ .hzzr)2 gns3operty of oxa36ikxc. ud v0,wn gj +l:i:,hjzf5 transition metals?
I. Catalytic behaviour
II. Coloured compounds
III. Variable oxidation states
A. $II$ and $III$ only
B. $I$ and $III$ only
C. $I$, $II$, and $III$
D. $II$ only