Which of the following animal pairs would you expect to have the most similar embryonic development?
human and jellyfish
horse and zebra
polar bear and penguin
iguana and shark

The correct answer is horse and zebra.

Horse and Zebra are members of class a Mammalia. A mammal develops from one celled zygote, which is a fusion product of an ovum or egg and a sperm.  After fertilization the zygote undergoes cleavage, increasing the number of cells. After repetitive division blastocyst are formed. The blastocyst is characterized by a group of cells, called the inner cell mass or embryo blast) and the trophoblast.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.