Answer :
The correct answer is B. Grasp the end of the tail. You should do what is described in D but if you just hold it buy the tip, there's a chance that it might fall of or that you might rip it off which can be bothersome both for you as a scientist and for the rat who would be traumatized and might not be usefull for research anymore.
Answer:
B. Grasp the end of the tail
Explanation:
Rat's tails should only be held at the base while holding its body at the same time.