Propyne on cyclic polymerisation gives

Acetylene reacts with dilute $H_2SO_4$ in the presence of $HgSO_4$ to produce .......

$HC \equiv CH$ $\xrightarrow[{excess}]{{CH_3MgBr}} \mathop {(A)}\limits_{\text{salt}} + \mathop {(B)}\limits_{\text{hydrocarbon}}$
$(A)$ $\xrightarrow[{excess}]{{CH_3I}} (C)$ $\xrightarrow[{(ii) H^{+} }]{{(i) NaNH_2}} (D)$

Which reactants are used to prepare $cis$ and $trans$ alkenes from alkynes?

$CH_3-C \equiv C-CH_3$ $\xrightarrow{H^{+}/KMnO_4, \Delta} A$ $\xrightarrow{(1) LiAlH_4, (2) H^{+}} B$
$B$ will be

$CH \equiv CH + HBr \to X$,the product $X$ is: