Choose the correct statement(s).
A. Successive enthalpies of transition elements do not increase as steeply as in the main group elements.
B. The magnitude of the increase in the second and third ionsiation enthalpies for the successive elements of transition series, in general, is much higher.
C. The lowest common oxidation state of transition metals is `+2`.
D. The second ionisation enthalpy of Cr and Cu are usually high.