When sound waves hit a solid surface they either reflect, refract, or absorb.
Echo's are caused by the reflection of sound waves.
Evidence for evolution, in other words evidence of common descent, include fossils, which have shown a (fairly) steady change in morphology over time for some species. An example would be horse hooves: we have fossils that show when they were still three toed, then two toed, then one toe in our present day horses. Another piece of evidence is vestigial organs. An example of vestigial organs is wings in some flightless birds, such as the kiwi. Their ancestors used it in order to fly across the marine barrier into New Zealand, but natural selection and random genetic drift made them quickly lose the ability to fly. Nonetheless, they still have their wings, however small. It can be assumed that eventually, their wings would be reduced to small stubs fused to other nearby bones, as has been observed in their cousins.
Answer:
A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution, such as height or skin color, are polygenic.
Explanation:
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The correct choice is increases your heart rate and respiration.
Your sympathetic nervous system increases your heart rate and respiration when confronted with a stressful event.
sympathetic nervous system also mobilizes body for action, increases breathing and sweating, makes pupils dilated ad lastly decreases stomach's activity.
