the answer is A,why not use tell me why ,thanks

題目：

the answer is A,why not use tell me why ,thanks
-your english teacher's spoken english is very standard,wang ping.
-it's no wonder.she ___ in the UK for a year as a visiting scholar.
A worked B has worked C had worked D has been working

解答：

---your english teacher's spoken english is very standard,wang ping.
---王平,你的英語老師所講的英文非常標準,
這句說明王平的英語老師現在已經在這裡教書了,沒在UK了
---it's no wonder.she ___ in the UK for a year as a visiting scholar.
---不足爲奇.她曾經作爲訪問學者在英國工作了一年.
這句說明她曾經是在英國工作了一年,而不是從過去一直到現在都是.強調一個過去的動作,所以選A.
B的話是現在完成時,是表示從過去到現在一直持續的動作,而文中並沒有這個意思