Задача 6.

Is it true that: a) if $H$ is a subgroup of $G$, then $e \in H$; b) if $H$ is a subgroup of $G$, then $H$ is a group; c) if $H$ is a subgroup of $G$ and $K$ is a subgroup of $H$, then $K$ is a subgroup of $G$; d) the union of two subgroups is a subgroup; e) the intersection of two subgroups is a subgroup?