The correct option is A may use utilitarianism occasionally but not as a guiding moral principle.
The author is critical of utilitarianism and admits it has several problems, but she does not reject it as an ethical theory. In fact, she concedes that it is useful in creating social policies and legislation. Therefore, the most logical inference is that she may use utilitarianism occasionally but not as a guiding moral principle. Choices b and c are therefore incorrect. Choice d is incorrect because nothing in the passage indicates how she feels about utilitarianism as a basis for social policy. The passage does not state that she believes most people do not really understand utilitarianism, so choice e is incorrect.