First, if you consider the example where $C$ is the zero matrix, you can eliminate option 1. and option 3.
You are left with the other two options. Note then that if 2. is correct, then obviously 4. is correct as well. (If the dimension is always at most $n$, then since $n\leq 2n$, the dimension is also always at most $2n$.)
It is all just about determining whether 2. holds.
However, if you know about the Minimal polynomial you realize, as @lee mentioned in the comments, that $C$ has to satisfy a polynomial of degree at most $n$ (since $C$ is an $n\times n$ matrix).
So among the set of matrices in $\{1, C, C^2 , \dots , C^{2n}\}$, you can have at most $n$ linearly independent matrices.
And so $\dots$