An electron collides with a free molecule initially in its ground state. The collision leaves the molecule in an excited state that is metastable and does not decay to the ground state by radiation. Let $K$ be the sum of the initial kinetic energies of the electron and the molecule,and $p$ be the sum of their initial momenta. Let $K^{\prime}$ and $p^{\prime}$ represent the same physical quantities after the collision. Then,

• A
  $K = K^{\prime}, p = p^{\prime}$
• B
  $K^{\prime} < K, p = p^{\prime}$
• C
  $K = K^{\prime}, p \neq p^{\prime}$
• D
  $K^{\prime} < K, p \neq p^{\prime}$