In the past,Many students did not know the importance of English.在这里为什么要加did,去掉did是否可以?did是什么词,在句子里充当什么成份?这个句子是不是属于一般过去时态?但是在一般过时里,在什么情况

I had many teachers in the past in the past,many people died of___(hungry) In the past many people died of _ (hungry). In the past people used many things___of money there are many pandas.用in the past 改写句子 I had many teachers in the past year 此句中有in the past year为何不用完成时 There were many green trees in this area in the past.(同义句转换)There ____ ____ _____ many green trees in this area in the past In the past several years,i had many chances to inspect many places of China The song____(sing) many times by the students in the past week The song____(sing) many times by the students in the past several months in the past造句 Memory in the past in the past two in the past翻译 ：in the past century in the past long in the past few Trapped in the past