NEED THIS QUICK!! Read the following scenario.

After getting their results in, a group of scientists went back and looked at their study. As planned, their experiment consisted of three groups. The first group received a new medicine at a normal dose, the second group received the medicine at half the dose, and the third group received the medicine at twice the dose.

Which of the following best describes what went wrong with the scientists’ study?

a. an improper experimental procedure

b. the lack of a control group

c. selection bias

d. human error

(its not a)