The number of stereoisomers possible for a compound of the molecular formula $CH_3-CH=CH-CH(OH)-CH_3$ is

Which of the following pairs represents stereoisomerism?

Match the following:

$A$. Acetaldehyde,vinyl alcohol	$1$. Enantiomers
$B$. Eclipsed and staggered ethane	$2$. Tautomers
$C$. $(+)2$-butanol,$(-)2$-butanol	$3$. Chain isomers
$D$. Methyl-$n$-propylamine and diethylamine	$4$. Conformational isomers
	$5$. Metamers

The correct statement$(s)$ about the compound given below is(are):
$A$. The compound is optically active
$B$. The compound possesses centre of symmetry
$C$. The compound possesses plane of symmetry
$D$. The compound possesses axis of symmetry

Maximum number of isomers of $C_4H_8$ are

The product of this reaction should be