The other answers which you've provided here shouldn't be correct. Although it does probably depend on th emethods which are being used so it perhaps isn't necessarily true that desalinaiton is cheaper.
Correct answer choice is:
C. Desalination provides water suitable for drinking.
The reclamation of effluents for soaking and obscure freshwater practices is swiftly emerging as an option to seawater desalination. Two membrane-based choices ready to use residue for water reuse, tertiary filtration (TF) of the effluent from a traditional activated sludge (CAS) method and a multicultural membrane bioreactor (MBR) are searched; in both instances, the level of approach can be complemented by reverse osmosis (RO). These choices are connected to desalination of seawater with both traditional multi-media layer filtration.
a. desalination is less expensive than...