Increasing order of stability
(a) `CH_(3)CH = CH- CHO`,
(b) `CH_(3) overset(+)(C )H- CH= overset(overset(H)(|))(C )- underset(..)overset(..)(O):^(-)`
(c ) `overset(+)( C)H_(2)- CH= CH- overset(overset(H)(|))(C )= O`

Explanation

(c ) `lt` (b) `lt` (a)