(b)
When, $\theta \in \left( 0,\ \frac{\pi}{4} \right)$
$\tan{\theta < \cot\theta}$
Since, $\tan{\theta < 1}$ and $\cot{\theta > 1}$
$\therefore\ \ \left( \tan\theta \right)^{\cot\theta} < 1$ and $\left( \cot\theta \right)^{\tan\theta} > 1$
$\therefore\ \ \ t_{4} > t_{1}$, which only holds in (b)