The seemingly effortless elegance of the dancer's performance masked years of rigorous training and meticulous attention to detail. This underscores that true mastery in any discipline often involves not only inherent talent but also a deep understanding of its underlying principles and a relentless dedication to the _____, despite their often being invisible to the casual observer.

设离散型随机变量X的分布函数为F(x)，已知F(x)在x=-1时为0.2，在x=2时为0.5，在x=5时为1，那么E(X)的值是多少？

在C++中，哪个关键字用于声明一个整型变量？

在选择排序中，算法的稳定性如何？

在应用数学公式时，以下哪种做法最有助于提高解题效率？