Complete the missing links $$(X),\ (Y)$$ and $$(Z)$$ by making appropriate choice.
$$CH_3COOH \xrightarrow{PBr/Br_2}X \xrightarrow{KCN}Y \xrightarrow{H_3O^+}Z$$:

1) $$X = CH_3COBr \,\,\,\,\, Y = CH_3COCN \,\,\,\,\, Z = CH_3COOH$$
2) $$X = BrCH_2COOH \,\,\,\,\, Y = {\underset{CN}{\underset{|}{C}H_2}}COOH \,\,\,\,\,Z = HOOC-CH_2COOH$$
3) $$X = BrCH_2COOH \,\,\,\,\, Y = CH_2(CN)COOH \,\,\,\,\, Z = {\underset{COOH}{\underset{|}{C}OOH}}$$
4) $$X = Br_2CHCOOH \,\,\,\,\, Y = Br_2C(CN)COOH \,\,\,\,\,\, Z = CH_3CH_2COOH$$