Assertion: Water used in hemodialysis is carefully purified before use.
Reason: The damaged kidneys cannot perform their intended function of removing impurities.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.