$D=\left(\frac{\lambda -1}{2},\frac{5+3}{2},\frac{\mu +2}{2}\right)$
$=\left(\frac{\lambda -1}{2},4,\frac{\mu +2}{2}\right)$
Direction ratios of AD are ($\frac{\lambda -1}{2},-2, 4-3,\frac{\mu +2}{2}-5$)

$i.e.(\frac{\lambda -1-4}{2},1,\frac{\mu +2-10}{2}$)
$i.e.(\frac{\lambda -5}{2},1,\frac{\mu +8}{2}$)
Now if we go by options (since the line AD is equally inclined to coordinate axes, its direction ratio are in ratio ($\pm 1 :\pm 1 : \pm 1$ )
We get that for $\lambda =7,\mu =10$ direction ratios of AD are $\text{1,1,1}\text{.}$