it forms covalent bonds by sharing electrons
The answer that goes in the blank is Division.
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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Answer:
Acute inflammation of the mucous membrane of the nose, with the discharge of mucus; a head cold.
Explanation: