A implies that there are a number of effective and inexpensive alternatives.
B suggests that blocking out salts is something that can already be done through the use of nanotechnology.
C claims that science is already capable of easily mimicking biological processes of desalination.
D implies that although there are known processes of desalination, a cost-effective solution is yet to be developed.
E suggests that despite it being challenging, mimicking biological processes is something that can already be done effectively and for affordable prices in Singapore.