The observation of tool-making among chimpanzees led several scientists to reconsider the definition of what it is to be human

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This statement is correct.

For a long time, humans believed that they and they alone could use tools, and using tools was used to distinguish human species from other species. If Chimpanzees can use tools too, then we either have to admit that they're human too or change our understanding of what human means.

Covalent bond is the correct answer