Paleontologists have discovered several ancestors of the modern horse.

Based on the skeleton, the skull, and the leg bones, which fossil is the oldest?

Which fossil is most like a modern horse?

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.

the answer is d p: cell, q: organ, r: organ system, s: tissue

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.