The second and third rows of transition elements resemble each other much more than they resemble the first row. explain why ?

Question

$\begin{array}{1 1}\text{(a)Due to fully filled d orbitals}\\\text{(b) Due to actinoid contraction, the atomic radii of the second and third row transition elements is almost same.}\\\text{(c) Due to lanthanide contraction, the atomic radii of the second and third row transition elements is almost same.}\\\text{(d) Due to fully filled f orbitals}\end{array} $