Which of the following can serve as the best title of the passage 9

A．have determined the full range of contaminants in the water supply
B．have ascertained the geographic extent of the water pollution
C．have developed new methods to measure water contaminants
D．have succeeded in preventing drinking water from being polluted

A．Altogether 95 different contaminants have been found in streams.
B．Nearly 80 percent of the streams surveyed contains only the familiar contaminants.
C．The most frequently detected contaminants are usually in low concentrations.
D．The average number of contaminants in each stream surveyed is seven.