Answer
D
Explanation
When you're taking someone else's pulse, you shouldn't use your thumb to take it because you might confuse your pulse for theirs.
A mental disorder is any disorder that affects the function of the brain making the patient incapable of normal life behavorior. Depression, anxiety, dementia and Schizophrenia are just a few. A mental disorder interrupts the normal function of the brain cause a multitude of issues and conditions. In order for a condition to be labeled mental disorder the condition has to cause dysfunction in the patients life.
D) an identical twin because they are basically the same person.