Give the major product of the following sequence of reaction

The aldehydes which will not form Grignard product with one equivalent of Grignard reagents are
$\left(\mathrm{A}\right)$

$\left(\mathrm{B}\right)$

$\left(\mathrm{C}\right)$

$\left(\mathrm{D}\right)$

Identify $A$ in the given chemical reaction.

Which of the following reactions is used for producing symmetrical alkane with double carbon atoms?