Graph B represents a line with a negative slope. In other words, the amount of Bacteria would decrease if their behavior mimicked this graph. Bill is incorrect.
Now, we are told that the amount of bacteria doubles each hour. This means the rate of change that occurs every hour cannot be expressed as a constant. For example, if we started with a single bacteria, after one hour we would have two bacteria (the difference between hour one and hour zero would be 1 bacteria). After two hours we would have four bacteria (the difference between hour two and hour one would be 2 bacteria). After three hours we would have eight bacteria (the difference between hour three and hour two would be 4 bacteria), and so on.
Because of this, the growth of the bacteria population cannot be represented via a line. So Daryl is also incorrect.
The graph that best represents this situation would be graph C.
In any case, neither of them is correct.