Assertion (A): Phenomena of dawn and dusk is experienced more in temperate regions.

Reason (R): The twilight continues as long as sun is 18° below the horizon.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Both A and R are true and R is the correct explanation of A.

Explanation — The twilight continues as long as sun is 18° below the horizon. In temperate regions, the angle at which the sun rises and sets is more slanted, so it takes longer to reach 18° below the horizon, hence longer dawn and dusk.