Which best describes the elements that comprise most of earth’s crust?

a.
a chemical combination of a few elements

b.
a single element, such as sulfur or gold

c.
a mixture of metals and nonmetals

d.
a chemical combination of about 100 elements

the answer will be a) proteins i believe

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.

"do a testcross with a homozygous recessive plant."

what are the options