Two particles of equal mass have velocities $\vec{v}_{1}=2 \hat{i} \mathrm{~m} \mathrm{~s}^{-1}$ and $\bar{v}_{2}=2 \hat{j} \mathrm{~m} \mathrm{~s}^{-1}$, First particle
has an acceleration $\vec{a}_{1}=(3 \hat{i}+3 \hat{j}) \mathrm{m} \mathrm{s}^{-2}$ while the acceleration of the other particle is zero. The centre of mass of the two particles moves in a path of
(a) straight line
(b) parabola
(c) circle
(d) ellipse