Assertion (A):The temperature at which vapour pressure of a liquid equal to the external pressure is called boiling temperature.
Reason (R): At high altitude atmospheric pressure is high.

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.