Which one of the following is ' d ' -block element?

The element in which last electron enters in $d$-orbital is called $d$-block element. The electronic configuration of the given elements are as follows $$\begin{aligned} \mathrm{Gd}(64) & =[\mathrm{Xe}] 6 s^2, 4 f^7, 5 d^7 \\ \mathrm{Hs}(108) & =[\mathrm{Rn}] 7 s^2, 5 f^{14}, 6 d^6\end{aligned}$$$$\begin{aligned} & \operatorname{Es}(99)=[\mathrm{Rn}] 7 s^2, 5 f^{11} \\ & \operatorname{Cs}(55)=[\mathrm{Xe}] 6 s^1\end{aligned}$$$ Thus, Hs is a d-block element.