Methyl vinyl ketone on reaction with $LiCuMe_2$ gives a major product,whose structure is

The major product formed in the following reaction is:

Which of the following compounds shows tautomerism?

Write the structures of the products of the following reactions:
$(i)$ $CH_3-CH=CH_2 \xrightarrow{H_2O/H^+}$
$(ii)$ (See image)
$(iii)$ $CH_3-CH_2-CH(CH_3)-CHO \xrightarrow{NaBH_4}$

Identify the structure of $B$ in the following reaction sequence:
$2,6-\text{dimethylcyclohexane-1,4-dione} + \text{ethane-1,2-diol}$ $\xrightarrow{H^+} A$ $\xrightarrow[2. H_3O^+]{1. LiAlH_4} B$

Compound '$A$' gives a positive test with $2,4-DNP$ and with $I_2/NaOH$. Compound '$A$' may be: