Which of the following statements is true?
a. both light waves and sound waves are mechanical waves.
b. both light waves and sound waves are electromagnetic waves.
c. sound waves are electromagnetic waves and light waves are mechanical waves. d. light waves are electromagnetic waves and sound waves are mechanical waves.

A light wave of any kind will always be transverse and electromagnetic. A sound wave of any kind will always be longitudinal and mechanical. Therefore, the answer is D: Light waves are electromagnetic waves and sound waves are mechanical waves.

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many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.