"Success, like self-worth, is something that must be determined by each individual according to the standards, beliefs, and values that they use to guide their life." meaning

True, theres is a crashcourse philospohy video on this. This is called the Nihilistic view.

The best paraphrase for the last paragraph of this section is C, because, according to this paragraph, doughnuts are now available in many different types and healthier options such as whole wheat doughnuts and companies have also started to try to reduce the fat in their doughnuts.  

Options A and D are true but they don´t paraphrase the meaning of the last paragraph. Option B is incorrect because this information isn´t mentioned in the text.