Answer:
B. It provides a clear definition of what the public has a right to expect from responsible engineers.
Step-by-step explanation:
Similar to licensed attorneys, doctors, accountants, etc., as licensed engineers, it is our ethical responsibility to provide engineering judgement based in the best interest of the public, i.e., not your employer, partner, colleague, because we serve the public first, and they have a right to expect us to do the right thing as trained, experienced professionals, because it is our duty and a privilege.
A is incorrect because the concept of strictly following professional code of ethics won't really keep you from legal troubles, because you still have judgement calls to make, and those could be end up being a mistake that that will cost a contractor or a client money, regardless of the decisions being ethical or not.
C is incorrect because following ethics won't play a part in raising the image of the profession because you can be an ethical saint, but still be rude and arrogant which will impact your image as an engineer far greater than being ethical. You can also make honest mistakes while following an ethical code of conduct, and it won't matter to the contractor/client who was negatively impacted if you were ethical or not.
D is incorrect because trust is built over time, based on numerous factors. Yes, ethics will play a role in building trust, but ultimately the public will only trust engineers who execute successful projects, time and time again. You can make an honest mistake and still lose their trust. You can blame contractors, vendors, etc. for making mistakes, and most people will see through your intent to maintain your "perfect" image, thereby causing them to lose their trust in you as an engineer.