A bullet of mass m and velocity a is fired in to a large block of wood of mass M . The final velocity of the system is

• A. <table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>M</center></td><td rowspan="2"></td><td rowspan="2">a</td></tr><tr><td style="text-align: center;">m + M</td></tr></table>
• B. <table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>m</center></td><td rowspan="2"></td><td rowspan="2">a</td></tr><tr><td style="text-align: center;">m + M</td></tr></table>
• C. <table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>m + M</center></td><td rowspan="2"></td><td rowspan="2">a</td></tr><tr><td style="text-align: center;">m </td></tr></table>
• D. <table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>m + M</center></td><td rowspan="2"></td><td rowspan="2">a</td></tr><tr><td style="text-align: center;">M</td></tr></table>