<span>air = a mixture of nitrogen, oxygen and some other bits
(pure) CO = carbon monoxide, a compound
pure water = H2O, a compound.</span>
Since the trait is dominant, it is possible for his parents to be heterozygous (Bb). So they have the trait but they have a gene they can pass on with out it. If both of his parents Bb then he could’ve gotten both recessive and therefore not receive the trait
It is soil after wind for example wind storm causes to soil erosion