Which of the following is true regarding extinction?
a. the rate of extinction is steady from clade to clade as are the number of species contained within a clade.
b. extinction that occurs in a relatively short period of time is referred to as background extinction.
c. single events or several causes working together to produce extinction in a short period is referred to as mass extinction.
d. if the rate of speciation in a clade is equal to or less than the rate of extinction, the clade will survive.

the right answer is a. skin cells forming from sunlight.

the liver is an organ endowed with a fantastic ability to regenerate

. thus, if a hepatectomy (ablation) of 70% of the hepatic mass is performed in the rat, there is complete recovery in 7 to 10 days.

prokaryotes are beings that have existed since the existence of life on earth, and do not come from another realm.

ribosomes are organelles that exist naturally in eukaryotes, either in free form or attached to the endoplasmic reticulum.

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answer: - b cells

explanation: -

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.