$C{\left(OH\right)}_4$  is unstable because a carbon atom cannot hold more than one – OH groups but  $Si{\left(OH\right)}_4$is a stable compound because 

$C{\left(OH\right)}_4$  is unstable because C cannot have more than -OH molecule, thereby it loses $H_{2}O$  molecules and convert into stable $C{O}_2$ molecule which contain strong  $p\pi -p\pi$  bonds.

Si-O bond is strong because of the larger size of the silicon atom and thus, the bond energy is also high for the Si-O bond. Also, silicon cannot form strong $p\pi -p\pi$ bonds like carbon.

Therefore, correct options are A and B