$+$ means 'is the brother of'
$-$ means 'is the sister of'

$\times$ means 'is the father of'

Which of the following means that $C$ is the son of $M$?

Let's decode option C: $M\times N-C+F$
Using the given operational codes:

1. $M\times N⟹M$ is the father of $N$.
2. $N-C⟹N$ is the sister of $C$. This means $M$ is also the father of $C$.
3. $C+F⟹C$ is the brother of $F$. This establishes that $C$ is male.

Since $M$ is the father of $C$ and $C$ is a male, it directly implies that $C$ is the son of $M$.