高三

In a sentence

• 我哥哥现在是高三学生，准备高考。

  My older brother is currently a senior in high school, preparing for the college entrance examination.

  Here, '高三' is used as a specific term referring to the third year (senior year) in a typical Chinese high school curriculum, demonstrating its academic usage.

• 高三学生的生活常常很忙，复习功课是首要任务。

  The lives of senior high school students are often very busy, as reviewing lessons is the primary task.

  In this sentence, '高三' again refers to the senior year of high school, emphasizing its connection with a period of intensive study and preparation.

• 高中三年的时光总是转瞬即逝，要珍惜每一天。

  The three years of high school always pass by quickly; cherish every day.

  Here, '高中三年' uses '高三' in a broader context, referring to the entire duration of high school years collectively rather than specifying the senior year.