The post-war explosion in the use of detergents (清结剂) was a prime cause for the deteriorating (恶化) condition of Thames twenty-five years ago. Between 1951 and 1961, detergent use increased three times. A tragic example of the results of this was when a man drowned because, though help was at hand, the would-be rescuers could not see him through the mass of foam. Previously, detergents had been of vegetable origin and caused no trouble. The new "hard" (technically, non-biodegradable 不能分解的) detergents contained elements which could not be degraded in the treatment plants sewage (污水) works. These detergents decreased the efficiency of plants by an estimated 30 percent. So when the waste water from the works was sent into the river, it still contained much "hard" detergent, which foamed or spread on the surface and greatly reduced the amount of oxygen naturally taken into the water. These detergents were also poisonous to fish. The threat became so serious that in 1957 the Standing Technical Committee on Synthetic Detergents held talks with government representatives, river authorities and manufacturers. Through friendly persuasion manufactures voluntarily agreed to phase out (逐步停止) "hard" detergents in favor of biodegradable ones which could be broken down during sewage treatment. A very marked improvement to the Thames, and some other rivers, quickly came on the heels of this application of cooperative common sense. Continuing guard is kept on the Thames: Specialists watch over the river as doctors might do for a patient. Samples are taken daily at high and low tide at twenty-nine points on a fortnightly cycle. Thus is the health of the river constantly monitored: Any minor illness is at once corrected, continuing improvement joyously recorded. The restoration of the tidal Thames is perhaps best demonstrated by the following simple table: Take the figure 900 as representing the general degree of pollution in 1950. Twenty-five years later it was 250. In 1980 it read 90 -- a reduction of pollution over thirty years by 90 percent. Justifiably we can speak of "the Thames saved". Which statement is TRUE according to the passage
A．The Thames has not been saved from pollution yet. B．The condition of the Thames was at worst in the 1950s. C．Few people are concerned about the pollution problems of the Thames. D．No one is certain what the main cause for the pollution of the Thames is.