题目内容：
More than forty thousand readers told us that they looked for in close friendships, what they expected __51__ friends, what they were willing to give in __52__, and how satisfied they were __53__ the quality of their friendships. The __54__ give little comfort to social critics.Friendship __55__ to be a unique form of __56__ bonding. Unlike marriage or the ties that __57__ parents and children, it is not defined or regulated by __58__. Unlike other social roles that we are expected to __59__—as citizens, employees, members of professional societies and __60__ organizations—it has its own principle, which is to promote __61__ of warmth, trust, love, and affection __62__ two people.
The survey on friendship appeared in the March __63__ of Psychology Today. The findings __64__ that issues of trust and betrayal（背叛） are __65__ to friendship. They also suggest that our readers do not __66__ for friends only among those who are __67__ like them, but find many __68__ differ in race, religion, and ethnic（种族的） background．Arguably the most important __69__ that emerges from the data, __70__, is not something that we found—but what we did not.
阅读短文，回答（51）题。 A．on
B．of
C．to
D．for
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