19.已知斜率为kkk的直线lll经过抛物线C:y2=4xC:y^{2}=4xC:y2=4x的焦点FFF,且与抛物线CCC交于A(x1A(x_{1}A(x1,y1)y_{1})y1),B(x2B(x_{2}B(x2,y2)y_{2})y2)两点,则下列说法正确的是((( )))