In the Three Domain system of taxonomy, living things are first placed in three groups based on the outstanding features of their cell structures. What aspect of cell structures do most animals and plants share in common to set them in the shared domain, “Eukarya”? A. cell structures defined by cell membranes
B. an undefined nucleus
C. chlorophyll structures
D. rigid cell walls

It is A

B is prokaryotes

C is only plants or cells that use photosynthesis and eukarya are broader than that

D is too specific as well as many eukarya don't have rigid cell walls

Explanation:

lesson summarykaryotypes a genome is the full set of all the genetic information that an organism carries in its dna. chromosomes arebundles of dna and protein found in the nucleus of a eukaryotic cell.