C. Narcolepsy is the answer
When the skin is exposed to ultraviolet rays, the skin produces a molecule that is turned into Vitamin D.
Sun is the source of ultraviolet rays important for Vitamin D production. Due to this reason, in the case of Vitamin D deficiency, it is recommended by doctor's to absorb sunlight by skin. The Vitamin D production occurs specifically by UV B rays rays which lie in the range of 290-315 nanometer.
The chemical 7-dehydrocholesterol absorbs these rays and convert to previtamin D3. Further, previtamin D3 isomerizes to Vitamin D. Other than sunlight, Vitamin D can be taken through diet. The sources include seafood like fish, fish oil, dairy products, beef liver etc. Vitamin D is required for bone and teeth formation, muscle contraction, immune system etc.
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<span>The option which is the least important to consider before choosing a fitness activity is B. the popularity of the activity. It doesn't really matter whether an activity is popular and if a lot of people are doing it, you should do whatever you want to do. So, your personal interest, the cost, and time commitment are things you need to consider before opting for an activity, and you don't have to think about its popularity really.</span>
Parasitism, that should be the correct answer for this question!
