Which of the following pairs of alkenes is an example of position isomers?

• A
  $but-1-ene$ and $2-methylprop-1-ene$
• B
  $but-1-ene$ and $2-methylbut-1-ene$
• C
  $but-1-ene$ and $but-2-ene$
• D
  $but-2-ene$ and $2-methylprop-1-ene$