The correct answer is C. Tissue
Explanation:
In the diagram, x is between organ and cell level. This implies this level of organization is smaller than an organ but no as small as one cell. In this context, the most suitable term to add to this level is a tissue because these are structures composed of specialized cells, which shows this level encloses cells. Also, a group of tissues forms an organ; this implies the organ is the level that follows the tissue. Examples of this include muscle tissue composed of muscle cells and that is part of organs including the heart.
A.) An allele is a version of a gene that can be expressed as a phenotype.
