The line graph $L(G)$ of a simple graph $G$ is defined as follows:
There is exactly one vertex $v(e)$ in $L(G)$ for each edge $e$ in $G$.
For any two edges $e$ and $e'$ in $G$, $L(G)$ has an edge between $v(e)$ and $v(e')$, if and only if $e$ and $e'$ are incident with the same vertex in $G$.
Which of the following statements is/are TRUE?
(P) The line graph of a cycle is a cycle.
(Q) The line graph of a clique is a clique.
(R) The line graph of a planar graph is planar.
(S) The line graph of a tree is a tree.
(A) P only
(B) P and R only
(C) R only
(D) P, Q and S only