Which of the following best describes a partially complete protein?

A partially complete protein is best described as having an unbalanced mixture of essential amino acids. Unlike complete proteins, which contain all nine essential amino acids in sufficient quantities, partially complete proteins lack one or more of these amino acids or have them in inadequate amounts. This results in an unbalanced profile, meaning that while they may provide some essential amino acids, they do not fully meet the body's needs when consumed alone.

In terms of the other choices, complete proteins are those that fulfill all essential amino acid requirements, which is not applicable to partially complete proteins. The idea that partially complete proteins are derived only from animal sources is inaccurate because there are many plant-based sources that are also partially complete, lacking some of the essential amino acids. Lastly, taste is subjective and not a defining characteristic of protein completeness; thus, the notion of being lacking any unpleasant taste does not pertain to whether a protein is complete or incomplete.