题型分类：推论题

原文定位：定位词：the Navajo ritual chants。利用定位词定位到第一段最后两句，说“我们所知的二十四首纳瓦霍圣歌可由多达500幅的沙画来表现。这些复杂的绘画作为辅助记忆的手段，指导歌手在仪式中的演唱，这些演唱可以持续九天。”可推测出，歌手需要绘画作为记忆辅助手段，那么这些表演应该是很难记住的。

选项分析：

C选项：“They are difficult to remember.”对应第一段最后两句“The twenty-four known Navajo chants can be represented by up to 500 sand paintings. These complex paintings serve as memory aids to guide the singers during the performance of the ritual songs, which can last up to nine days.”

A选项：“There is a large number of them.”文中最后一句提到沙画的数量是500幅，并未说the Navajo ritual chants数量很多。张冠李戴。

B选项：“Each of them corresponds to a particular sand painting.”文中无此信息，无中生有。

D选项：“They do not take long to perform.”，最后一句说…, which can last up to nine days.”持续九天。选项与原文描述不符。