Let $\displaystyle K$ be a field. For any $\displaystyle l \in \{1,2,...,n\}$, let $\displaystyle Col(l)=\{A=[a_{ij}] \in Mat_n(K): a_{ij}=0, \forall j \not= l\}$. Prove that $\displaystyle Col(l)$ is a minimal left ideal in $\displaystyle Mat_n(K)$.

I know how to prove that $\displaystyle Col(l)$ is a left ideal in $\displaystyle Mat_n(K)$, but having trouble with the minimality part of the proof. Can I get some help please?