When my mother called me last night,_______ .(A)I had been playing video games for three hours)(B)I was playing video games.請問哪個對？

When my mother "called" me yesterday, I "was playing" video games.
過去簡單式是一個「點」，過去進行式是一條「線」，兩者的時序關係：點在線之上。
action verb會有發生的時間點。call／play都是action verb。

I "had been playing" video games for three hours when my mother "called" me yesterday.
句子裡有for how long時，需要一個「計時的終點」，使用when當連接詞時，它所帶出的副詞子句提供了主要子句action verb的「終點」。這句也是正確的寫法，但強調的是當時的「結果」：已經三小時。過去完成式與過去完成進行式的不同在後者強調事件還在繼續發生。

(A) had been playing---for---
For unfinished, lasting actions, uncompleted, the past perfect continuous is used together with adverbials beginning with "for".
(B)In example B, two actions happened in the past at the same time. The past continuous tense is used for the longer action=playing for three hours. Ans.(B).