Let the four couples be (assuming heterosexual peeps :P)
$M_1F_1,$ $M_2F_2,$ $M_3F_3,$ $M_4F_4$
If $M_1$ is chosen, $F_1$ must not be chosen and vice versa.
This is true for all the couples.
So, select exactly one member from each couple.
=> $_{1}^{2}\textrm{C}*_{1}^{2}\textrm{C}*_{1}^{2}\textrm{C}*_{1}^{2}\textrm{C}=16$
Option D