题目选项分析

Early in the twentieth century, Lake Konfa became very polluted. Recently fish populations have recovered as release of industrial pollutants has declined and the lake's waters have become cleaner. Fears are now being voiced that the planned construction of an oil pipeline across the lake's bottom might revive pollution and cause the fish population to decline again. However, a technology for preventing leaks is being installed. Therefore, provided this technology is effective, the fears are groundless.

Which of the following, if true, most seriously weakens the argument?

【选项】Since the beginning of the twentieth century, non-native species of fish have been introduced into the lake and now make up a considerable proportion of its overall fish population.