Explain how a thumbtack is designed so that you do not have to use a lot of force to push it through paper or the surface of a bulletin board?

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.

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