6. As shown in the figure, the graph of the function $y=-\frac{1}{2} x+2$ intersects the $y$-axis at $M$, and the $x$-axis at $N$. Points $A, B$ are on $MN$, and their projections on the $x$-axis are $A_{1}, B_{1}$ respectively. If $O A_{1}+O B_{1}>4$, then the relationship between the area $S_{1}$ of $\triangle O A_{1} A$ and the area $S_{2}$ of $\triangle O B_{1} B$ is ( ).
(A) $S_{1}>S_{2}$
(B) $S_{1}<S_{2}$
(C) $S_{1}=S_{2}$
(D) Cannot be determined
6. (A).

Let $O A_{1}=x_{1}, O B_{1}=x_{2}$. Then $x_{1}0 .
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