When I was doing this question, I was also totally tempted by A and had originally selected it. What made me end up ruling it out is that it's basically saying that every single obligation is a promise, which absolutely is does not need to be true for this argument to hold. In the premises, they talk about someone having a promise, which implies an obligation, but obligation does not imply a promise. Promises are just a subset of obligations. In other words, this answer choice is just too strong for what we need.

You're correct that typically "properly drawn" is used in SA questions, but this specific question stem asks, "Which of the following principles must be assumed...," which implies necessity. If it were an SA question, it would read something like, "Which one of the following principles, if assumed, would allow for the psychologist's conclusion to be properly drawn?"

Hope this helps!