Which of the following must an engineer consider when designing a car's tires?

When designing tires for a car, an engineer must consider the materials that will be used to fabricate the tires ... both the suitability of the materials for the purpose, and their cost.

For example, the engineer should not design car tires to be made of glass or of silk, since these would not hold up well when driving on concrete roads, and they would need to be replaced too often.

For another example, he should not design car tires to be made of gold or polished diamond, since these would be beyond the price range of most car owners, and also, these tires would be very susceptible to being stolen by nefarious and dishonest individuals in the middle of the night.

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I hope this answer is helpful.  The question you posted is a very difficult one, because there are no answer choices listed, and also because the question has the mysterious unknown term "the following" in it.

a and b sometimes have a positive value

no

sodium is solid at rt