Larger number of oxidation states are exhibited by the actinoids than those by the lanthanoids, the main reason being
(a) More reactive nature of the actinoids than the lanthanoids
(b) 4f orbitals more diffused than the 5f orbitals
(c) Lesser energy difference between 5f and 6d than between 4f and 5d orbitals
(d) More energy difference between 5f and 6d than between 4f and 5d orbitals