An organic compound 'A' on treatment with NH3 gives 'B' which on heating gives 'C', 'C' on treatment with Br2 in the presence of KOH produces ethylamine. Compound 'A' is

CH3COOH CH3CH2CH2COOH CH3CH(CH3)COOH CH3CH2COOH

CH3CH2COOH

The correct answer is option 4. CH3CH2COOH