下课铃是中国最强音上课铃是黑色星期天
[xià kè líng shì zhōng guó zuì qiáng yīn shàng kè líng shì hēi sè xīng qī tiān]
'The dismissal bell is China’s strongest sound, while the class bell is a black Sunday.' Here, it uses a very colloquial expression to compare school life: the freedom at the end of the day against the less pleasant aspects such as being tied up by the schedule during class time.