5775 时态 - 过去不完成式

    过去不完成式通常代表一个连续或重覆的行动, 现在时态可译为 "they are
    asking," 而过去不完成式则译为 "they kept on asking."

    不过在"to be,"动词中, 过去不完成式则表示去过一个单一的事件,
    而不是连续或重覆的动作.

5775 Tense - Imperfect

    The imperfect tense generally represents continual or repeated
    action.  Where the present tense might indicate "they are
    asking," the imperfect would indicate "they kept on asking."

    In the case of the verb "to be," however, the imperfect tense
    is used as a general past tense and does not carry the
    connotation of continual or repeated action.