Refer to the following passage.
In recent years, shark attacks in U.S. waters have received wide attention. Are such attacks a growing threat to swimmers and surfers?
Statistics suggest not. The rate of attacks per number of swimmers has not increased over time. What has increased is the popularity of aquatic sports, such as surfing, sail boarding, and kayaking. More people are in the water these days, and therefore the chances of a shark encounter increase. Still, to keep the issue in perpective we should remember that there were only six fatal shark attacks in U.S. coastal waters from 1990 to 2000.
Q> According to the author, which of the following has NOT increased over time?
(A) the total number of shark attacks in U.S. waters
(B) the popularity of aquatic sports
(C) the number of fatal shark attacks in U.S. coastal waters
(D) the rate of shark attacks per number of people in the water
(E) the estimated shark population in U.S. coastal waters