Question

One student is investigating the cause of the unusual smell of water in wells of a location. What should be done to investigate the cause of the contamination of well water?

A study all events in the location during the past one year

B question secondary sources about the events in the location

C ask gas companies in the location to hire experts to check leakages

D record information about the land surface and location of the polluted wells


PLEASE JUST TELL ME WHICH ONE IS IT??