Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D on the ANSWER SHEET. (10 points)
　　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 instruct 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._____ 

A.Until

B.Unless

C.Although

D.When