The correct answer is:
C. They create less sympathy for the creature by making him a mindless beast.
The film adaptations are basically trying to make this a Horror story, creating a reckless creature, make him speak incorrectly, make him a terrorific beast. While in the book they describe him physically as a beast, but with human behaviour, eloquent speaking, adequate manners etc. The real idea in the book is centralized in showing the reader Frankenstein could be more human in the inside, than the real human who created him.