I lunch when I learned that former British prime minister Margaret Thatcher had passed awa

问题补充：

I lunch when I learned that former British prime minister Margaret Thatcher had passed away.

A. ate

B. had eaten

C. was eating

D. were eating

答案：

A. ate

B. had eaten

(答案→)C. was eating

D. were eating

解析：表示过去某一时间正在进行的动作，用过去进行时，故选C。