$15.$ A slender rod $($mass $=$ M$)$ is at rest. If a bullet $($mass $=$ m$)$ is fired with a velocity of vb$,$ the angular momentum of the rod and bullet just after impact will be $\_\_\_\_\_\_\_\_.$ A$)$ m vb $+$ M$(0\mathrm{.}5)$$2$ B$)$ m$(0\mathrm{.}5)2$ $2+$ M$(0\mathrm{.}5)2$ $2$ C$)$ m$(0\mathrm{.}5)2$ $2+$ M$(0\mathrm{.}5)2$ $2+(1/12)$ M $2$ D$)$ zero