Because it is for school related topics. Join a chat room that allows you to say as you wish. Like your mom would say: Their house, Their rules.
<span>Why are nutrients essential?
They play an important role in many body processes, are used to ensure our physiological needs, such as growth, development <span>and metabolism.</span></span>
This would exclude Digestion, being a factor in efficiency. All of the others are correct, except for answer D.