The answer to this question it is very hard for me

In dna, only the_ varies from one nucleotide to another. base phosphate sugar amino acid

According to theories of how life began, how did early organic molecules begin to separate from the outside world? a: specialized enzymes were required b: chains of amino acids created a barrier c: formation of microspheres or vesicles d: rna catalyzed the formation of membranes

High blood pressure occurs when there is too much blood flowing through the blood vessels at one time. by changing the amount of water in the blood, blood pressure can change. the excretory system can to lower blood pressure.which would most likely occur in the kidney? a)more water would be transferred from the nephron.b)less water would be absorbed into the nephron.c)the amount of water in the bladder would decrease.d)the amount of water in the blood would increase.