Assertion $(A)$: Rapidly changing temperatures can be measured by thermocouples.
Reason $(R)$: The thermal capacity of the junction of a thermocouple is very small.

• A
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$
• B
  Both $(A)$ and $(R)$ are true but $(R)$ is not the correct explanation of $(A)$
• C
  $(A)$ is true but $(R)$ is false
• D
  $(A)$ is false but $(R)$ is true