Identify the type of isomerism exhibited by the following structures:
$H_3C-CH=CH-CH_3$ (cis-but$-2-$ene) and $H_3C-CH=CH-CH_3$ (trans-but$-2-$ene).

• A
  $Position$ isomerism
• B
  $Geometrical$ isomerism
• C
  $Optical$ isomerism
• D
  $Functional$ isomerism