2.已知椭圆C:x22+y2=1C:\frac{x^2}{2}+y^2=1C:2x2+y2=1的左焦点是F1F_{1}F1,过F1F_{1}F1的直线l:y=x+ml:y=x+ml:y=x+m与圆:x2+y2=4x^{2}+y^{2}=4x2+y2=4交于AAA,BBB两点,则∣AB∣\vert AB\vert∣AB∣的长为((( )))