Which of the following lanthanoids show +2 oxidation state besides the characteristic oxidation state +3 of lanthanoids?

(a) Cerium $\left(Z=57\right)\Rightarrow$  Electronic configuration =$\left[Xe\right]4f^{1}5d^{1}6s^2$   Oxidation state of Ce = +3,+ 4
(b) Europium$\left(Z=63\right)\Rightarrow$   Electronic configuration =  $\left[Xe\right]4f^{7}5d^{0}6s^2$ Oxidation state of Eu = +2,+3
(c) Ytterbium $\left(Z=70\right)\Rightarrow$  Electronic configuration =$\left[Xe\right]4f^{14}5d^{0}6s^2$   Oxidation state of Yb = +2,+ 3
(d) Holmium $\left(Z=67\right)\Rightarrow$  Electronic configuration =  $\left[Xe\right]4f^{11}5d^{0}6s^2$  Oxidation state of Ho = +3