$4.$In a circular linked list

a$.$components are all linked together in some sequential manner.

b$.$there is no beginning and no end.

c$.$components are arranged hierarchically.

d$.$forward and backward traversal within the list is permitted.

$5.$The data structure required to evaluate a postfix expression is

a$.$queue

b$.$stack

c$.$array

d$.$linked$-$list

$6.$In a linked list with n nodes, the time taken to insert an element after an element pointed by some pointer is

a$\mathrm{.}0(1)$

b$\mathrm{.}0($n$)$

c$\mathrm{.}0($log n$)$

d$\mathrm{.}0($n $1$og n$)$