Why are populations with high levels of genetic diversity more stable than populations with low levels of genetic diversity?

a.
populations with high levels of genetic diversity are less likely to interbreed with other populations.
b.
populations with high levels of genetic diversity are more likely to have individuals with traits that them survive if conditions change.
c.
populations with high levels of genetic diversity are less likely to have high levels of variation in alleles.
d.
populations with high levels of genetic diversity are more likely to have individuals that will undergo natural selection if conditions change.