In a random mating population in equilibrium,which of the following brings about a change in gene frequency in a non-directional manner?

$A$ very important consequence of geographical isolation is ........

Natural selection can lead to . . . . . . .
$(a)$ stabilisation
$(b)$ genetic drift
$(c)$ directional change
$(d)$ disruption
Choose the correct answer from the options given below:
$(A)$ $(a)$, $(b)$ and $(c)$ only
$(B)$ $(a)$, $(c)$ and $(d)$ only
$(C)$ $(a)$, $(b)$, $(c)$ and $(d)$
$(D)$ $(a)$ and $(c)$ only

The peppered moth $(Biston \text{ } betularia)$, the black-coloured form became dominant over the light-coloured form of moth in England during the industrial revolution. This is an example of

According to Hugo de Vries,speciation due to mutation is saltation,which means-

Comment on the statement that 'evolution and natural selection are end result or consequence of some other processes but themselves are not processes'.