What are dark lines ​

An absorption line in an electromagnetic spectrum, appearing as a black line at visible wavelengths. ... 'Each element or compound in the sample absorbs particular wavelengths of light, resulting in one or more dark lines on its spectrum. '

Explanation:

An absorption line in an electromagnetic spectrum, appearing as a black line at visible wavelengths

Explanation:

population. population is the number of people or animals in a particular place. an example of population is over eight million people living in new york city.

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synapse nervous system