If tan A = n tan B and sin A = m sin B, then the value of cos A is

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