D is the answer! I just had this question and it was right !
The answer is the muscular system
The answer to this question is histidine. Histidine i<span>s an </span>α-amino acid<span> involved in the biosynthesis of </span>proteins. The structure of histidine includes<span> an </span>α-amino acid<span>, a </span>carboxylic acid group<span>, and an </span>imidazole<span> side chain. Histidine was initially thought to be </span>essential<span> only for infants; however, it has since been found to be essential for adults too.</span>
Answer:
Are specialized
Explanation:
Multicellular organisms are composed of more than one cell, with groups of cells differentiating to take on specialized functions.