考虑一个变分问题，其目标是最小化泛函J(u) = ∫(u'(x))^2 dx + ∫f(u(x)) dx，其中u(x)是待求解的函数，f(u)是一个光滑的非线性函数。若u(x)的边界条件为u(0) = u(1) = 0，以下哪个条件是u(x)的极值条件？

在顺序存储结构的队列中，队列的最大容量N是指什么？

Which of the following is a fixed collocation in English?

A recent outbreak of a preventable disease occurs in a community with low vaccination rates. What is the most critical action that health authorities should take to control the outbreak?

在进行超车时，驾驶员应打转向灯的时间要求是？