Which of the Following Accurately Describes the Problem of Confounding

Which of the following accurately describes the problem of confounding by severity in a drug safety study?

A) The more severe side effects of drugs cause people to stop taking the drug and the drug appears less harmful than it really is.
B) When health care providers prescribe one drug more commonly than others for patients with a more severe form of disease, the drug will look more harmful than it really is.
C) When patients have previously experienced severe side effects from a similar type of drug, they will not be put on a drug, thus making it look less harmful than it really is.
D) When there are severe side effects from a drug, people over-report them, making a drug look more harmful than it really is.