英语被动语态的从句的时态,是和主动语态的从句的时态一样吗?例如,The students must finish all

英语被动语态的从句的时态,是和主动语态的从句的时态一样吗?例如,The students must finish all tne exercises before school is over.的被动语态中,before school is over要改变时态吗?如果要改,是什么时态?We should turn on the lights when the charity show starts.的被动语态中,when the charity show starts要改变时态吗?如果要改,是什么时态?不难的.这一块老师刚讲,有的问题我还不太明白.