The correct option is
C Fall
A compound noun is made up of two or more existing words, to form a completely new word in meaning.
Option C: 'Water' forms a compound noun with 'fall': 'waterfall'.
A 'waterfall' is 'a cascade of water falling from a height, formed when a river or stream flows over a steep incline'.
Hence, option C is correct.
Options A, B and D: 'Water' does not form any compound noun with 'food', 'stick' or 'out'.
The words 'waterfood', 'waterstick' and 'waterout' do not exist in standard English language.
Hence, options A, B and D are wrong.