你的第一句最好加上last,這樣你就明白了：
It's two years since I LAST worked in Beijing.---------不在那里工作已經(jīng)兩年了.
第二句只強(qiáng)調(diào)在過去,到底是怎樣的過去無所謂,與“今天“沒有任何關(guān)系,所以只用”一般過去時(shí)“.如果是had worked,句子應(yīng)該是這樣的：
He had worked in Africa on wild animals for eight years before he came to be our biology teacher last year.--------過去的過去,用”過去完成時(shí)“.
Our work not finished == as our work hadn't been finished yet -------你的是獨(dú)立主格結(jié)構(gòu),我的是原因狀語從句結(jié)構(gòu).-------獨(dú)立主格結(jié)構(gòu)需要去掉助動(dòng)詞had 和been,保留真正動(dòng)詞.