$$ H_{1} : \mu_{D} > 0 \ (\mu_{1} > \mu_{2}) \ \rightarrow \ t_{0} > t_{\alpha} (n-1) $$
$$ H_{1} : \mu_{D} < 0 \ (\mu_{1} < \mu_{2}) \ \rightarrow \ t_{0} < - t_{\alpha} (n-1) $$
$$ H_{1} : \mu_{D} \neq 0 \ (\mu_{1} \neq \mu_{2}) \ \rightarrow \ | \ t_{0} \ | > t_{\alpha/2} (n-1) $$