(c)
O OH
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \parallel \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |$
$CH_{2}CH_{2} - CH_{2} - C - CH_{3} \rightleftharpoons CH_{3}CH_{2}CH_{2} - C = CH_{2}$
ketoform enol form