求这句英文句子的语法错误在哪里?
those who wish to be a musician should bear in mind that much practice is required and that a great deal of it is decidedly unexciting
补充，这个句子只有一个语法错误。
我刚开始觉得 those和 a musician 一个单一个复，不行
但是后面的that又很奇怪