Surface runoff, its quite obvious in the picture
If H+ would have to dissociate from a substance and must be the only positive ion in the solution that substance must be an acid.
CH3CHO is an aldehyde called acetaldehyde.
CH3CH2OH is an alcohol called ethanol
CH3OCH3 is an ether called dimethyl ether.
and finally, the answer CH3COOH is a weak acid called acetic acid.
