Trust is a tricky business. On the one hand, it’s a necessary condition (1)_____ many worthwhile things: child care, friendships, etc. On the other hand, putting your (2)_____ in the wrong place often carries a high (3)_____.

    (4)_____, why do we trust at all? Well, because it feels good. (5)_____ people place their trust in an individual or an institution, their brains release oxytocin, a hormone that (6)_____ pleasurable feelings and triggers the herding instinct that prompts humans to (7)_____ with one another. Scientists have found that exposure (8)_____ this hormone puts us in a trusting (9)_____ : In a Swiss study, researchers sprayed oxytocin into the noses of half the subjects; those subjects were ready to lend significantly higher amounts of money to strangers than were their (10)_____ who inhaled something else.

    (11)_____ for us, we also have a sixth sense for dishonesty that may (12)_____ us. A Canadian study found that children as young as 14 months can differentiate (13)_____ a credible person and a dishonest one. Sixty toddlers were each (14)_____ to an adult tester holding a plastic container. The tester would ask, “What’s in here?” before looking into the container, smiling, and exclaiming, “Wow!” Each subject was then invited to look (15)_____. Half of them found a toy; the other half (16)_____ the container was empty and realized the tester had (17)_____ them.

    Among the children who had not been tricked, the majority were (18)_____ to cooperate with the tester in learning a new skill, demonstrating that they trusted his leadership. (19)_____, only five of the 30 children paired with the (20)“ _____ ” tester participated in a follow-up activity.

答案精析：根据上下文可知，condition与many worthwhile things: child care, friendships, etc存在因果关系，it代指句首的trust。此句意为：对诸如保育、友谊等很多重要的事情来说，信任是一个必备条件。for表示“对……来说”，与condition搭配意为“是……的条件”，选项C符合题意。

错项排除：condition不与on和from搭配，A、D错误。根据上述分析可知，condition与many worthwhile things不是从属关系，B错误。