I believe the correct answer is A. They must be clearly stated, not simply understood.
It isn't good to presume that the other party can read our minds when it comes to expectations in relationships. Without clearly stating our wishes, needs, and intentions, we risk misunderstanding with our partners. As for other options, B isn't true because nothing may substitute contact; expectations differ very much from one relationship to another; even if they are realistic, they don't necessarily contribute to a relationship's success.
