Assertion $(A)$: The upper surface of the wing of an aeroplane is made convex and the lower surface is made concave.
Reason $(R)$: The air currents at the top have smaller velocity and thus less pressure at the bottom than at the top.

• A
  Both $A$ and $R$ are true and $R$ is a correct explanation for $A$
• B
  Both $A$ and $R$ are true but $R$ is not a correct explanation for $A$
• C
  $A$ is true,$R$ is false
• D
  $A$ is false,$R$ is false