3. A line $l$ is drawn through the fixed point $P(2,1)$, intersecting the positive direction of the $x$-axis and the positive direction of the $y$-axis at points $A$ and $B$, respectively, such that the area of $\triangle A O B$ (where $O$ is the origin) is minimized. The equation of $l$ is ( ).
(A) $x+y-3=0$
(B) $x+3 y-5=0$
(C) $2 x+y-5=0$
(D) $x+2 y-4=0$