The rotation of the $0.9 m$ arm $OA$ about $O$ is defined by the relation $\theta = 0.15t^2$, where $\theta$ is expressed in radians and $t$ in seconds. Collar $B$ slides along the arm in such a way that its distance to $O$ is $r = 0.9 - 0.12t^2$, where $r$ is expressed in meters and $t$ in seconds. After the arm $OA$ has rotated through $30$ degrees, what is the total acceleration of collar $B$ (relative to $O$)?

A. $(-0.359e_r - 0.391e_\theta)$ $m/s^2$
B. $(-0.391e_r - 0.359e_\theta)$ $m/s^2$
C. $(0.391e_r + 0.359e_\theta)$ $m/s^2$
D. $(0.369e_r + 0.648e_\theta)$ $m/s^2$
E. $(-0.369e_r - 0.648e_\theta)$ $m/s^2$
F. $(0.648e_r -0.369e_\theta)$ $m/s^2$