Ralph is looking at a blood vessel under a microscope as part of his study about the cardiovascular system. He notices that the vessel contains blood and has valves. What is the blood vessel that he is observing?

6. in the dna double helix, how are the two strands of dna held together? a. chemical bonds between base pairs hold the two strands of dna together. b. hydrogen bonds between the base pairs hold the two strands of dna together. c. hydrogen bonds between sugar groups and phosphate groups hold the two strands of dna together. d. chemical bonds between sugar groups and phosphate groups hold the two strands of dna together.

What was the land like over 500 million years ago? what was under the sea?

The dense layer of connective tissue that surrounds an entire skeletal muscle is the