A study was conducted on the effect of daytime running lights on cars. Researchers gathered data from a random sample of 3,248 drivers and measured quite a few variables, in addition to the explanatory variable of daytime running lights and the response variable of less accidents. According to a newspaper article summarizing the study, those cars that had daytime running lights were more likely to be operated by drivers who were confident and attentive. Drivers whose cars did not have daytime running lights were about 22% more likely to have an accident. What conclusion can we draw from this study? Explain.

a. We can infer a cause-and-effect relationship because the sample was selected randomly.
b. We cannot infer a cause-and-effect relationship because we do not have a control group.
c. We can infer a cause-and-effect relationship because multiple variables were included.
d. We cannot infer a cause-and-effect relationship because treatments were not assigned randomly.
e. We cannot infer a cause-and-effect relationship because the treatments imposed were not blocked correctly.