1 It's two years since I （worked）in beijing,but I still miss

1 It's two years since I （worked）in beijing,but I still miss many things and people there.这个题中括号里为什么不用 has worked?
2 Walter offered us a lift when he was leaving the office,but our work(not finished),we refused his offer.括号中为什么不是has not been finished?
3 The man was arrested by the police for spreading the rumor here and there (that)there would be a shortage of salt in the province.括号中that如何解释是什么从句?
会几道说几道啊谢谢了