When doing medical research with human subjects, which FOUR limitations are unavoidable?

A. It's often impossible to repeat trials on the same subjects.

B. Subjects may report an inaccurate medical history.

C. It can be difficult to control all possible variables.

D. It's impossible to come up with testable scientific questions for human subjects.

E. There are ethical or privacy concerns to consider.

Option B, C, D and E

Explanation:

While conducting research on human being, following conditions must be fulfilled

a) The subject must be made aware of the risk and result of the study

b) Subject must be aware of the study objective, time duration and post study impacts

c) Subject must be compensated for any injury caused during the study

d) Informed consent must be taken from the subject

e) The subject must beware of the possible uncontrollable scenarios. Also the test conducted must be testifiable on human being

f) The ill effects of the study can be anticipated if the result obtained are worthy enough

Considering the above facts, option B, C, D and E are unavoidable