As a band instructor at an elementary school, I require my students to turn in practice sheets signed by their parents so I can be sure they are putting in enough time.
作为一个小学的乐队指挥，为了确保学生投入足够的时间练习，我要求他们上交由他们父母签字的练习单。

I had to laugh, however, when one parent wrote on her child's sheet, "Practiced 17 minutes, but it seemed like hours.
可是有一次，一位家长的签字把我逗乐了。练习单上写着：“练习了17分钟，但犹如几个时辰。”

【注释】

(1) band n.乐队

(2) instructor n.指挥

(3) turn in上交；归还

(4) signed by their parents:由他们的父母签名的。这是一个分词短语作定语修饰sheets.

(5) so I can be sure they are putting in enough time:这样我才能确定他们投入了足够的时间。这是so that 引导的目的状语从句，其中that省略。