The principles and standards of ethical supply chain management conduct includes the principle:
a) promote competitive relationships with suppliers.
b) social competence.
c) protect confidentiality.
d) be true to yourself.

D) Be true to yourself.

Explanation:

The Institute of management have about 10 standards for supply management conducts. these standards are derived from 3 major principles which are;

Integrity in Your Decisions and Actions

Value for Your Employer

Loyalty to Your Profession.

The 10 standards are; Impropriety, conflict of interest, influence, responsibility to your employer, supplier and customer relationship, sustainability and social responsibility , reciprocity, confidential and proprietary information , professional competence and applicable laws, regulations and trade agreements .

there is no mention of be true to yourself.

i go with [ a