Answer:
You can't see the blood vessels themselves because vision depends on a process that makes it impossible to see things that are stationary with respect to the retina. Light receptors in the retina respond only to changes in light reaching them, not to a steady image.
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The answer should be: codeine, hydrocodone, oxycodone or tramadol
Opioid drugs are frequently used to treat pain. Acetaminophen, aspirin or NSAIDs drug used for mild to moderate pain. The mild opioid will be used in moderate to severe pain while a strong opioid will be used in severe pain. Strong opioid that could be used for severe pain would be morphine, methadone, oxycodone, or fentanyl
Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).
Selective breeding on food crops may create stronger, and more healthy crops. The idea is to find your best crops, and breed them with other crops sharing the traits you want.