Which of the following pairs of molecules are metamers?

• A
  $CH_{3}OCH_{2}CH_{3}$ and $CH_{3}CH_{2}OCH_{2}CH_{3}$
• B
  $CH_{3}CH_{2}CH_{2}OH$ and $CH_{3}CH(OH)CH_{3}$
• C
  $CH_{3}CH_{2}CH_{2}CH_{3}$ and $(CH_{3})_{2}CHCH_{3}$
• D
  $CH_{3}CH_{2}OCH_{2}CH_{3}$ and $CH_{3}OCH_{2}CH_{2}CH_{3}$