Answer: board-certified "pathologist" (physician).
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You have to first make some observations and then ask a question. Then you make a hypothesis (or guess) what the answer is - do the experiment to see if you're right!
The first step begins with: A. the mouth.
~Hello There!~
The answer is serotonin.
Hope This Helps You!
Good Luck :)
Have A Great Day ^_^
- Hannah ❤
