Answer
$CH_3CH_2OH$ has highest boiling point
Work Step by Step
Hydrogen bonding occurs when $H$ is covalently bonded to highly electronegative atoms ($N, O, F$) and can interact with a lone pair on another electronegative atom.
The answer is $CH_3CH_2OH$ because it has $H$ bonding (due to $H-O$ bond). $H$ bonding makes molecules connect to each other stronger => raise the molecules boiling point.
$HI$ and $H_2S$ do not have $H$ bonding. Ether has $C-O-C$ group not $O-H$ so there isn't any $H$ bonding either.
