答案：C
解析：根据文中“The first group was told that the man 'liked to steal'. One week later the first group remembered a higher bill...”可知，科学家告诉第一组这个男人喜欢偷东西，让学生们认为这个人是坏人，这种先入为主的观念导致他们记住的账单金额更高，C选项正确。

答案：C
解析：文中提到“people watched a film and were asked: 'How fast was the white car going when it passed the barn (仓库) while travelling along the country road?' Actually there was no barn in the film.”，问题中提到了“barn”，而实际上电影中没有，这个问题中的“barn”就是给学生的暗示，导致部分学生以为看到了谷仓，所以“hint”指的是问题中的“barn”一词，C选项正确。

答案：A
解析：文中提到“Most people 'clearly remember' that it's si, while their childhood textbooks say it's shi. It shows how unreliable (不可靠的) our memory can be. According to US psychologist Faith Brynie, memories can be influenced by imagination, belief and time.”，人们对“si”和“shi”的记忆不同，表明记忆会受想象、信念等影响，即情感等因素会决定人们的记忆，A选项正确；B选项与原文“the version (版本) of si is also more widespread than shi”不符；C选项“always unreliable”过于绝对；D选项文中未提及。

答案：A
解析：文章主要讨论了记忆的不可靠性，通过多个实验和例子说明人们的记忆会受到各种因素的扭曲，甚至会记住从未发生过的事情，A选项“Are you really sure?”（你真的确定吗？）能够引发读者对自己记忆可靠性的思考，适合作为文章标题；B选项“Have you forgotten yet?”（你已经忘了吗？）侧重遗忘，不符合主旨；C选项“ What should be remembered?”（应该记住什么？）文中未提及；D选项“How is the memory improved?”（如何提高记忆力？）与文章讨论记忆不可靠性的主题不符。