An organic compound A upon reacting with $NH_3$ gives $B$.On heating, B gives $C$.$C$ in presence of $KOH$ reacts with $Br_2$ to give $CH_3CH_2NH_2.A$ is :

Question

$\begin{array}{1 1} (1) CH_3COOH \\ (2) CH_3CH_2CH_2COOH \\ (3) CH_3 - CH - COOH \\(4) CH_3CH_2COOH \end {array}$