Which one among the following pairs of ions cannot be separated by $H_2S$ in dilute hydrochloric acid?

Question

(a) $Bi^{3-}, Sn^{4+}$
(b) $Al^{3+}, Hg^{2+}$
(c) $Zn^{2+}, Cu^{2+}$
(d) $Ni^{2+}, Cu^{2+}$