4 pics 1 word level 33

IPhone version. Not sure if it's different to the android version but there's a picture of someone riding a bike up a mountain, a stack of pebbles, some guy with an 8 pack and what I think is a walnut.

4 letters. Letters given are: D D B Z A R K S F N H M

Hard i think!

A person riding bike, stack of pebbles, 8 pack and walnut