The following figure is a diagram showing parts of the human eye. Identify $P, Q$,and $R$ from the options given below.
$\quad\quad P\quad\quad\quad Q\quad\quad\quad R$

• A
  Iris $\quad$ $\quad$ Lens $\quad$ $\quad$ Retina
• B
  Iris $\quad$ $\quad$ Lens $\quad$ $\quad$ Choroid
• C
  Lens $\quad$ $\quad$ Iris $\quad$ $\quad$ Sclera
• D
  Lens $\quad$ $\quad$ Iris $\quad$ $\quad$ Choroid