they worked three days_____before ago long for哪一个?before和ago有什么区别,简洁些,

It was three years since they worked here.这是高二的一道改错题,答案是把worked 改成 had worked这个答案对吗? they worked three days_____before ago long for哪一个?before和ago有什么区别,简洁些, They had a rest after they worked about three hours.(改为同义句)其实要填空是：They stopped____ ____a rest after_____about three tours. They worked very h___ they have worked in the factory for three years,（对划线部分提问)how many have they worked in the factory?但是答案用的是how many呀？所以我有点想不通，答案是不是错的啊 They worked hard at___(sing). They worked ___________(hard).急 They worked hard yesterday afternoon.用worked hard 提问 What do they often da? They worked very hard this morning. they worked very hard this morning they worked very hard this morning They worked in a company ___made computers. they have three pencils.对three提问 where did your mother do worked three years ago改错 They were clever and they worked out the problem__(easy). they worked so hard that they overfulfilled their plan. 英语翻译Three teenarers decided to do volunteer work during the school holidays.They worked for the organization save the children.It helps children round the world.Save the children had a painting comprtition for patients between 10 and 13years