According to the kinetic molecular theory of gases, which of the following statements are correct?
$a$) The actual volume of the molecules is negligible in comparison to the empty space between them.
$b$) Collisions of gas molecules are inelastic.
$c$) At any particular time, different particles in the gas have the same speed and same kinetic energies.
$d$) Pressure is exerted by the gas as a result of the collision of the particles with the walls of the container.

• A
  $a$ and $b$ only
• B
  $a, b$ and $c$ only
• C
  $a$ and $d$ only
• D
  $a, b, c$ and $d$