Answer: Double blind clinical trial
Explanation:
The situation that is seen here is double blind clinical trail in which neither the participant nor the practitioner knows who is receiving the treatment.
This is used to prevent biasing in the experiment which is caused due to demand characteristics or placebo effect.
Here, in this situation the dog handlers and the experimental observer both were blinded to identify the breath sample.
The answer is All of the above
It means that they are near sighted. I know this because I am also near sighted. Which makes it hard for me to read road signs from a far away distance sometimes. Hope this helps!!!
