The last time I Jane she cotton in the fields. A. had seen; was picking B. saw; picked C. had seen; picked D. saw; was picking 为什么选D

The last time I Jane she cotton in the fields.
A. had seen; was picking B. saw; picked C. had seen; picked D. saw; was picking
为什么选D

因为是过去时
所以要用saw
后来又在讲说他最后一次看见jane的时候她在干什么.
所以是was picking