17. The small, dense region indicated in Figure 7–2 by the letter D is called the
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the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

i'd have to say the answer is probable the second option "the geosphere interacting with the atmosphere"

garbage disposal because lysosomes dispose of old cell parts like garbage disposals dispose of old food.