$(2)$ For the following statements about red$-$black trees, please justify the CORRECT

statements. $,$ A subtree of a red$-$black tree is itself a red$-$black tree.

ii$,$ The sibling of an external node is either external or it is red.

iii, There is a unique $(2,4)$ tree associated with a given red$-$black tree.

iv$.$ There is a unique red$-$black tree associated with a given $(2,4)$ tree.