Final answer:
Nuts are the source of protein that does not contain all nine essential amino acids, making them an incomplete protein. Animal-based products like beef, chicken, eggs, and milk typically provide complete proteins. option b is correct.
Step-by-step explanation:
The source of protein that does not contain the nine essential amino acids is b. nuts. Proteins that have all nine essential amino acids are called complete proteins. These are typically found in animal-based products such as beef, chicken, eggs, and milk. On the other hand, plant-based proteins such as nuts, grains, and beans are known as incomplete proteins because they lack one or more of the essential amino acids.
Vegans, in particular, need to be mindful of their protein intake and often have to combine different plant proteins to ensure they get all the essential amino acids necessary for good health. For example, rice and beans eaten together can provide a complete protein profile. This is because different plant sources can complement each other's amino acid profile.