The passage indicates that the pattern that characterizes a bacterium's motion changes in response to A. The kinds of chemical attractants present in different concentration gradients. B. The mechanism that the bacterium adopts in determining the presence of an attractant. C. The bacterium's detection of changes in the concentration of an attractant. D. The extent to which neighboring bacteria are engaged in tumbling. E. Changes in the intervals of time that occur between the bacterium's measurement of the concentration of an attractant.