Assertion $(A):$ A person goes to high altitude and experiences 'altitude sickness' with symptoms like breathing difficulty and heart palpitations.

Reason $(R):$ Due to low atmospheric pressure at high altitude, the body does not get sufficient oxygen.

In the light of the above statements, choose the correct answer from the options given below.

• A

  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$

• B

  Both $(A)$ and $(\mathrm{R})$ are true but $(\mathrm{R})$ is not the correct explanation of $(A)$

• C

  $(\mathrm{A})$ is true but $(R)$ is false

• D

  $(\mathrm{A})$ is false but $(\mathrm{R})$ is true