A frictionless circular wire of unit radius is fixed on the horizontal plane. Two-point particles of unit mass start moving simultaneously from point $A(\theta=\frac{\pi}{2})$ with identical uniform angular speeds in opposite directions, and meet again at point $B(\theta=-\frac{\pi}{2})$. During this time, which of the following figures schematically represent the magnitude of the total linear momentum P of the system, as a function of $\theta$? [Image Placeholder]