A. read; was falling　B. was reading; fell　C. was reading; was falling　D. read;fell

　　答案B.句中的as = when, while，意为"当……之时"。描述一件事发生的背景时，用过去进行;一个长动作发生的时候，另一个短动作发生。句意为 "在她看报纸时，奶奶睡着了。"句中的 fell (fall的过去时)，是系动词，后跟形容词，如：fall sick。

　　过去进行时和一般过去时的区别

　　一.一般过去时叙述旧事，过去进行时描述背景。

　　A、一般过去时

　　1)叙述过去状态、动作或事件

　　He went to Beijing the other day.(带具体时间)

　　2)表示过去的习惯

　　a) would ,used to与过去时

　　would 表间断性不规则的习惯，常带频率时间

　　used to 表一贯性有规律的习惯

　　They used to meet and would sometimes exchange one or two words.

　　b) Would 用于文中不用于句首，只表过去习惯。

　　Used to 表今昔对比的含义，叙述习惯动作可与would 换用。

　　When he was a boy , he would often go there . (叙述过去)

　　She isn't what she used to be. (今昔对比)

　　c) 表示状态时一般只用used to

　　Tom used to be fat /There used to stand a tree there. (状态)

　　d) was (were) used to +ving表示“合适于，适应于…..”

　　He used to work at night . (“习惯”表经常)

　　He was used to working at night. (习惯表适应)

　　3)表示过去的经历，平行动作，依此事件用一般过去时。

　　He sat there and listened to the radio.(依此发生)

　　B. 过去进行时