Given the ellipse $\frac{x^2}{3}+y^2=1$ with left and right foci $F_1, F_2$ respectively, the line $y=x+m$ intersects $C$ at points $A$ and $B$. If the area of $\triangle F_1AB$ is 2 times the area of $\triangle F_2AB$, then $m=$\\
A. $\frac{2}{3}$\\
B. $\frac{\sqrt{2}}{3}$\\
C. $-\frac{\sqrt{2}}{3}$\\
D. $-\frac{2}{3}$