Correct answer is option no. (a) because

Hugo de Vries, based on his work on evening primrose brought forth the idea of mutations. He believed that mutation caused speciation and hence called it saltation (Single step large mutation).

Option (a) is incorrect because mutations are sudden (random) and directionless.

Option (b) is incorrect because mutation theory was proposed by Hugo de Vries.

Option (c) is incorrect because Darwinian variations are small and directional changes, but they are not related to mutation theory of evolution.