Summary
Trust requires mutual respect. Moreover, trust is essential to any long-lasting relationship, personal or professional. Personal relationships, such as marriage or friendship, additionally require natural affinity. If a personal relationship is to last, it must be supported by mutual respect and affinity.
Notable Valid Inferences
A personal relationship supported only by trust and mutual respect will not be long lasting.
A personal relationship supported only by natural affinity will not be long lasting.
A personal relationship supported only by natural affinity will not be long lasting.
A
A friendship supported solely by trust and mutual respect will not be long-lasting.
Must be true. As shown below, a long-lasting personal relationship requires natural affinity in addition to trust and mutual respect. 
B
In the context of any professional relationship, mutual respect presupposes trust.
Could be false. This answer choice confuses sufficiency for necessity. We know that mutual respect is a necessary condition for trust. It is possible for a necessary condition to occur without the sufficient condition.
C
If a personal relationship is supported by mutual respect and affinity, it will last a long time.
Could be false. This answer choice confuses sufficiency for necessity. We know that mutual respect and affinity are necessary conditions for a personal relationship to be long-lasting. It is possible for a necessary condition to occur without the sufficient condition.
D
Personal relationships, such as marriage or friendship, are longer-lasting than professional relationships.
Could be false. The stimulus tells us several necessary conditions for these relationships to be long-lasting, but the stimulus does not give us any information to infer which relationships are longer-lasting than others.
E
Basing a marriage on a natural affinity will ensure that it will endure.
Must be false. The stimulus tells us that personal relationships, such as marriage, require mutual respect in addition to natural affinity.
Summary
The use of phrases like “as so-and-so said” or “as the saying goes” suggests that the following quote has just been illustrated. Such phrases are inappropriately used when an apparent counterexample has just been given.
Notable Valid Inferences
We’re looking for an answer choice where the quoted phrase directly contradicts the scenario previously described in the stimulus.
A
Fatima was a mathematician who often thought about unsolved problems of mathematics, although it was unpleasant to be reminded that most would probably remain unsolved in her lifetime. As the saying goes, “Strange how much you’ve got to know before you know how little you know.”
Could be true. The quoted phrase does not directly contradict Fatima’s experience. By being reminded most problems would probably remain unsolved in her lifetime, it’s possible that Fatima knows how little she knows.
B
Harold’s friends were surprised when he revealed that he had left his wallet at home and asked that someone lend him money. But he had done the same thing many times before. As Halliard said, “The force of selfishness is as inevitable and as calculable as the force of gravitation.”
Could be true. The quoted phrase does not directly contradict Harold’s experience. It is possible that Harold was being selfish when repeatedly leaving his wallet at home.
C
The best model of vacuum cleaner was the most expensive on the market, but it would have made Roger unhappy to purchase it. For although he never wanted anything but the best, he was also quite frugal, and would never have forgiven himself for spending the money. As the saying goes, “A penny saved is a penny earned.”
Could be true. The quoted phrase does not directly contradict Roger’s experience. Even though Roger wants the best, it is possible that he is still frugal because he believes in spending money wisely.
D
Sharon loved cats, but her husband was allergic to them. Still, he was occasionally willing to accompany her to cat shows. As the saying goes, “Shared lives mean shared loves.”
Could be true. The quoted phrase does not directly contradict Sharon’s husband’s experience. Even though he is allergic to cats, it is possible that he attends the cat shows because he wants to share the experience with Sharon.
E
Raoul spent a year planning and preparing for a fantastic ski trip. He enjoyed his ski trip greatly until he broke his leg and had to spend two weeks in the hospital. As the saying goes, “All’s well that ends well.”
Must be false. The quoted phrase directly contradicts Raoul’s experience. Raoul’s ski trip did not end well, he suffered a broken leg and spent significant time in the hospital.