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, those fears are groundless.
The argument depends on assuming which of the following?

【选项】The species of fish that are present in Lake Konfa now are the same as those that were in the lake before it was affected by pollution.