18

【解析】形容词辨析。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. 意为“在所有没有被戏弄过的孩子里面，大多数的孩子在习得一种新技能的时候与测试者的合作是怎么样的”，demonstrating that they trusted his leadership表明这些孩子信任他的领导，既然信任他们就是愿意与其合作，故选择B willing，be willing to为固定搭配，意为“愿意”。