$M$ has a son $Q$ and a daughter $R.$ He has no other children. $E$ is the mother of $P$ and daughter-in-law of $M.$ How is $P$ related to $M?$
- $P$ is the son-in-law of $M$
- $P$ is the grandchild of $M$
- $P$ is the daughter-in-law of $M$
- $P$ is the grandfather of $M$