问题补充：
--- I phoned you at six yesterday afternoon, but nobody answered.
--- Oh, I a walk with my parents near the river.
A. am taking
B. was taking
C. took
D. will take
答案：
A. am taking
(答案→)B. was taking
C. took
D. will take
解析：句意：-我昨天下午六点给你打电话，但是没人接。-哦，我那时正在和我的父母在河边散步。昨天六点正在做某事，过去某一时刻正在做某事，要用过去进行时态，主语是I，所以系动词用was。故选B.
