Passage I
Two measures of water quality are the number of Escherichia coli bacteria present and the biotic index, BI (a numerical value based on the type，diversity, and pollution tolerance of aquatic invertebrate animals). Both of these measures can be affected by water flow.
E.coli levels that are above 100 colonies formed per 100 mL of water indicate reduced water quality. Figure 1 shows the E. coli levels on 5 collection days at Sites l and 2 in a river.
Table 1 shows how water quality rating varies with BI. Table 2 shows the average BI of each site during the collection period.
Figure 2 shows the water flow at each site on the 5 collection days.
1. If an E. coli level of over 400 colonies formed per 100 mL of water is unsafe for swimming, on which of the following collection days and at which site would it have been unsafe to swim？
Your Answer is
Correct Answer is B
Explanation
Looking at figure 1, only when the abscissa is Site 1 Day 30, the ordinate E. coli colonies exceeds 400, so the answer is B