Daylight (photopic) vision and colour vision are functions of $P$,while twilight (scotopic) vision is a function of $Q$.
$\quad\quad \quad P\quad\quad\quad Q$

• A
  Rods $\quad\quad$ Rods
• B
  Cones $\quad\quad$ Cones
• C
  Cones $\quad\quad$ Rods
• D
  Rods $\quad\quad$ Cones