Two angles can be supplementary, if both are

Option (a) $\to$  if both are acute angles, let the two angles be $xandy$  $x<90°andy<90°$

(supplementary angles : Two angles whose sum is $180°$ )

Adding them $x+y<90+90$

                         $x+y<180$

Here, $x,y$  are not supplementary

Option (b) , both are obtuse,

$\Rightarrow x>90andy>0$

On adding $x+y>90+90$

                    $x+y>180$

$x,y$  are not supplementary

Option (c) , both are right angles

Let $x=90°$  $y=90°$

On adding , $x+y=90°+90°$

                      $x+y=180°$

Here,  $x,y$  are supplementary

Option (d) , Straight angles

$x=180°$ , $y=180°$

On adding $x+y=180+180$

                    $x+y=360°$

Here, $xandy$  are not supplementary