Answer
The first two columns of $AB$ will be equal.
Work Step by Step
Assuming that $AB$ is defined (i.e., that $A$ is an $m\times p$ matrix and $B$ is a $p\times n$ matrix), the definition of matrix multiplication gives $AB=\begin{bmatrix}A\vec{b}_{1}&A\vec{b}_{2}&\cdots&A\vec{b}_{n}\end{bmatrix}$.
Since $\vec{b}_{1}=\vec{b}_{2}$ (i.e., the first two columns of $B$ are equal), it must also be that $A\vec{b}_{1}=A\vec{b}_{2}$.
