求这句英文句子的语法错误在哪里?

题目

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

答案

those who 跟复数``
bear in mind 后面是 并列的宾语从句,由and或but所连接的两个引导的宾语从句时,第一个从句中的that可以省,第二个从句中的that不能省；