What is the best description of organisms of the precambrian era?
a . land plants and animals
b . dinosaurs and primates pice mammals
c . single celled organisms and soft, boneless animals
d . ferns and flying reptiles

Option C, Single celled organisms and soft, boneless animals

Explanation:

The Precambrian era refers to the first geologic time frame and thus it refers to  time frame which is some billion years old. During Archean period of Precambrian era,  single celled /unicellular and simple form of organisms originated such as protozoans (including amoeba, euglena, and paramecium). These organisms developed with time and by the late Precambrian era soft bodied multi-cellular organisms like jellyfish, worms . moss etc. originated.  

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.

c. live where it’s cold and icy