A, In or on water answers:
Scuba diving.
Kayaking.
Waterskiing.
White water rafting.
Paddleboarding.
B, in the air answers:
Ziplining.
Parascending.
Bungee-jumping.
C, on land answers:
Trekking.
Moutain-biking.
Horse-riding.
Which activities are difficult to put into one category?
Sightseeing. - You can sightsee above or on land, maybe even on water.
Canyoning. - Canyoning involves swimming or climbing, but it's never just one option.
I hope this helped.