According to Ross's theory,

A. there is no truth about how we ought to behave.

B. there is no mechanical way to determine how we ought to behave.

C. moral rules tell us exactly how we should behave in all situations.

D. it is self-evident how we ought to behave in certain situations.

D. It is self-evident how we ought to behave in certain situations.

Explanation:

Sir William David Ross was a British philosopher known by numerous accomplishments, such as the translations of Aristotle's work and the formulation of a new ethical theory.

In this theory, Ross suggested that there are some critical rules or duties that should be followed, except if/when they conflict. These rules are also considered to be self-evident. He defined them as facie duties, which are: fidelity, gratitude, reparation, justice, beneficence, non-maleficence and self-improvement