题干
Bob took a photo of his girlfriend while she _________ at the party.
A：dances
B：was dancing
C：has danced
D：is dancing
答案(点此获取答案解析）
B
Bob took a photo of his girlfriend while she _________ at the party.
A：dances
B：was dancing
C：has danced
D：is dancing
，点迹间各段长度已标在图上．若要求得该过程中小车运动的平均加速度，下列计算公式中最合理的是：（ ）
