Which statement best explains why each river has its own set of characteristics? Rivers flow downhill, pulled by gravity toward the sea.
Rivers interact with the ecosystems through which they pass.
Rivers absorb oxygen from the atmosphere as they flow downhill.
Rivers have climates that are determined by the biomes they flow through.

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explanation:

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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.

i think its white blood cells

i hope this