eg.There are a great many of online celebrities on the stage， I know none of them. 舞台上有许多网红，但是我一个也不认识。
由最后一段的倒数第二句话“You must also keep an open eyes on its date of publication because travel is very practical matter and many things change quickly in the 21st century.”可知出版的日期要注意，因为在21世纪的今天，很多事情的变化很快，故答案选D。
a number of， the number of。cause 指造成某一事实或现象的直接原因，后接of sth./doing sth，reason用来解释某种现象或结果的理由，后接for sth./doing sth. the reason for being late。
