When doing medical research with human which four limitation are unavoidable

1- It's often impossible to repeat trials on the same subjects. 2-Subjects may report an inaccurate medical history. 3-It can be difficult to control all possible variables. 4-It's impossible to come up with testable scientific questions for human subjects.

Explanation:

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the "dirty dozen" chemicals banned in an international treaty are formally known as persistent organic pollutants, or pops. the united nations environment program provided this background on what they are and what they can do to humans and wildlife.

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