I think it is D
Hope the answer is right!
Which of the following is always a component of allergies?
Out of all the answers shown above the one that best represents the one that is always a component of allergies is answer choice A) histamine.
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The answer is obsessive-compulsive disorder. Compulsive and usually unwanted thoughts and actions (rituals) are the common features of the disorder. Although OCD is usually associated with repeating the actions over and over, such as obsessive hand-washing or having to flick a light switch a certain number of times, many people who suffer from OCD struggle with frequent unwanted thoughts and images.