Answer alveoli and blood vessels
The respiratory bronchioles have single alveoli off their walls. ... The respiratory bronchioles lead into alveolar ducts, (which are surrounded by smooth muscle, elastin and collagen), which lead into the alveolar sacs. These have several alveoli, surrounded by blood vessels - from the pulmonary system.
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Answer:
The color of the fur is the phenotype
The genetic combination of alleles that determine the fur color is called the genotype
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An Endothermic Reaction ☺