Which of the following best explains why air is considered a natural resource?
a. air is expensive to produce and keep clean.
b. air is a raw material for biological processes supplied by the earth.
c. air can be processed to generate expensive chemicals.
d. none of the above

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modern american cars are not available due to trade restrictions

abu bakr, was a senior companion and—through his daughter aisha—a father-in-law of the islamic prophet muhammad. abu bakr became the first openly declared muslim outside muhammad's family. abu bakr served as a trusted advisor to muhammad.