The angle between the pair of lines whose equation is $4{\mathrm{x}}^2+10\mathrm{xy}+{\mathrm{my}}^2+5\mathrm{x}+10\mathrm{y}=0$ is

• A

  ${\tan }^{-1}(3/8)$

• B

  ${\tan }^{-1}(3/4)$

• C

  ${\tan }^{-1}\{2\sqrt{25-4\mathrm{m}}/(\mathrm{m}+4)\},\mathrm{m}\in \mathrm{R}$

• D

  None of these