答案：D

题目分析：it 指代句中music。这是一个省略关系代词that/which的定语从句。完整结构：Music should be taught routinely in schools because of the benefits that/which it can have on the development of the brains of young children.将整个句子换成“Music should be taught routinely in schools because it(music)can have benefits on the development of the brains of young children”就更容易理了。句意：音乐应该成为学校的常规的教学科目，因为音乐对青少年智力的开发大有裨益。