B. because they are not manufactured by the body
Certain amino acids are called essential amino acids because they are not manufactured by the body.
Amino acids are monomeric units of proteins. They are important building blocks in living organisms.
Some amino acids are manufactured in our body and are called non-essential amino acids while some cannot be produced by our bodies and called essential amino acids.
Essential amino acids are got from external sources of food. They include the following: Histidine, isoleucine, leucine, threonine, methylalanine etc.
Learn more about essential amino acids at: https://brainly.com/question/8019625
