20.
what makes up the backbone of a dna molecule?
ribose and deoxyribose
nucleic acids
rna molecules
sugars and phosphates

Sugars and phosphates  

Explanation:

DNA is deoxyribonucleic acid.

The backbone is based on a repeated pattern of a sugar group (deoxyribose) and a phosphate group.  

The image below shows one straightened-out strand of DNA with a backbone of alternating sugars and phosphates.

A is wrong. There is no ribose in DNA.

B is wrong. The nucleic acids A, C, G, and T join one strand of DNA to the other.

C is wrong. There is no RNA in DNA.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs

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