In discussions in class, people would answer this question by seeing how often they smile or laugh in response to stimuli, by measuring seratonin levels in the brain etc.
If asked in the exam (AQA AS Psychology), what is the one answer to this question that is guaranteed to be correct and worth a mark.
(I know that they probably won't ask this but I am just looking for what answer that most people can agree is correct).
I don't know if this made sense so.. yeah.