Why Don't Recessive Alleles That Cause Severe Disorders Disappear from Human

Why don't recessive alleles that cause severe disorders disappear from human populations?

A) new alleles can arise by mutation.
B) in heterozygotes, the dominant allele suppresses the recessive one but does not eliminate its presence.
C) in heterozygotes, although the trait associated with the recessive allele is not demonstrated, the allele may be passed on to offspring.
D) some recessive traits are not lethal nor do they interfere with reproduction.
E) all of these.