Assertion (A): The average temperature of the Earth has been rising. Reason (R): The greenhouse effect traps the Sun's heat within the Earth's atmosphere.

• Both (A) and (R) are true, and (R) is the correct explanation of (A).
• Both (A) and (R) are true, but (R) is not the correct explanation of (A).
• (A) is true, but (R) is false.
• (A) is false, but (R) is true.