How can marijuana affect a driver?

Answer: D — All of the above

Marijuana affects a driver by causing drowsiness, impairing their ability to accurately estimate time and distance, and slowing down their reaction time. Therefore, all of the given options are correct, making option D the correct answer. Option A is incorrect because it only mentions one effect of marijuana on a driver, while option B only mentions the impaired time and distance estimation. Option C is also incorrect as it only mentions the slowed reaction time, omitting the other effects caused by marijuana. Overall, option D provides a more comprehensive understanding of how marijuana can affect a driver.