Carbon dioxide is a gas,whereas silica is a solid because ...........

• A
  $CO_2$ consists of discrete covalent molecules,whereas silica has a continuous tetrahedral network structure.
• B
  $CO_2$ molecules are lighter than $SiO_2$ molecules.
• C
  $CO_2$ is more acidic than $SiO_2$.
• D
  The melting point of silica is very high.