Why do adaptations occur?

Given below are two statements.
Statement-$I$: Elimination of particular alleles from a population due to natural disasters is called genetic drift.
Statement-$II$: Sudden temporary heritable change in the gene is called point mutation.
In the light of above statements,choose the most appropriate answer from the options given below:

In the $1850$s,before industrialization in England,which type of moth was more abundant?

State the factors affecting the process of speciation.

Which is the most important factor for the evolution of a new species?

The Darwinian variations are