Dominant traits tend to be observed more frequently because
a.)only organisms with dominant traits can breed.
b.)dominant traits mask recessive traits.
c.)recessive traits mutate into dominant traits.
d.)organisms with recessive traits are extinct.

B, dominant traits mask recessive traits. Dominant traits aren't called dominant for nothing ;)
Let's say someone has the dominant allel A and the recessive one a, you observe the dominant one. If someone has twice dominant allel A, you observe the dominant one once again. The only time you'll observe the recessive one is when someone inherits the recessive one from the father as well as the mother.

D.) domain, kingdom, phylum, class, order, family, genus then species