where (表地點）
補答：
既然,您對答案不滿意.讓我詳細講解.以前給學生講課,強調的是語感,多給學生練類似的經典口語,臺詞之類.今天破例,I will give u a more detailed answer.
首先（_____ he worked）是一個定語從句修飾前面的office,說明是什么樣的office,是他工作的office.office 又回答了前句的where(Where did you meet him just now).顯然,用where引導一個定語從句,而且where的先行詞是office.
其次,選B,C或D的話,它們(which,that,the one)在從句中都是work的賓語（A,WHERE不是,where是做狀語）.而在英語當中work 表示工作（動詞）的時候,是不及物動詞,是不能有賓語的.
work要接上賓語,做及物動詞,就是使工作的意思（而不是工作,是使別人或東西工作）.
如：
To cause to work:
使工作：
works his laborers hard.
讓他的工人努力工作
如果選了Which,that或the one,給native speaker的感覺就是：他讓他的辦公室工作了.而這是不合邏輯的.
舉例：It was the disco where she found her boyfriend.
It was China where the couple adopted a child.
It was Shanghai where he worked.
I can't find Mr Smith.Where did you meet him just now?
--It was in his office _____ he worked.
A.where B.which C.that D.the one