Darwin wrote, "it at once struck me that under [specific environmental conditions] favorable variations would tend to be and unfavorable ones to be . The result of this would be the formation of new species.

The answer is "preserved" and "destroyed".

Fixing it would be: "favorable variations would tend to be preserved and unfavorable ones to be destroyed".

Explanation:

Here, Darwin was talking about the theory of evolution by natural selection.

This was first formulated in his book "On the Origin of Species" in 1859. He described evolution as 'the process by which organisms change over time as a result of changes in heritable physical or behavioral traits". Changes that allow an organism to better adapt to its environment and develop better offsprings.

While natural selection is often described as survival of the fittest, it simply means the ability of an organism to survive and reproduce as a result of phenotypic changes.

It is after the favourable variations are preserved and unfavorable ones are destroyed that new species form which is evolution.

for the comment!

i would pick a. i think this is more of a personal question though.