Assertion:After the appearance of oxygen in the atmosphere, methane and ammonia began to disappear.
Oxygen is involved in forming ozone layer.
A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion
B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
C. Assertion is true, but Reason is false
D. Assertion is false, but Reason is true