Well for "Hiking and Bird Watching" this would NOT be the correct option because bird watching offers no kind of physical activity.
Nor would it be "Fishing and Swimming" because while swimming is a nice way to get some activity, fishing is NOT due to its lack of movement.
"Fishing and Camping" are BOTH laid back activities where you don't recieve any activity. So this is NOT the correct answer.
Leaving you with the last option which contains two very, vigorous ways to get some activity. So the CORRECT answer would be D. Rock Climbing and Hiking.