A research paper, primarily utilizing statistical analysis, demonstrates a positive correlation between the frequency of a particular linguistic construction and the perceived level of formality in written communication. However, the paper also acknowledges instances where this correlation doesn't hold true. Which of the following scenarios most likely represents a situation where this positive correlation would be weakest?

以下哪个公式表示函数 f(x) 在点 x0 处的导数定义？

在大跃进运动中，片面追求高速度的主要问题是什么？

在自然语言处理系统中，字符串的存储和检索效率直接影响系统性能。以下哪种存储结构在处理动态变化的字符串集合时，能够提供更好的性能？

为了将某人从催眠状态中唤醒，以下哪种做法最有效？