Let $A$ be an $n \times n$ real matrix. It is known that there are two distinct $n$-dimensional real column vectors $v_{1}, v_{2}$ such that $A v_{1}=A v_{2}$. Which of the following can we conclude about $A?$
- All eigenvalues of $A$ are non-negative.
- $A$ is not full rank.
- $A$ is not the zero matrix.
- $\operatorname{det}(A) \neq 0$.
- None of the above.