Two particles of equal mass are projected from the ground with speed $v_1$ and $v_2$ at angles $\theta_1$ and $\theta_2$ as shown. The center of mass of the two particles

Question

a) will move in parabolic path for any value of $v_1,v_2, \theta_1$ and $\theta_2$

b) can move in a vertical line.

c) can move in a horizontal line.

d) will move in a straight line for any values of $v_1,v_2, \theta_1$ and $\theta_2$