[译] 在舞会上她介绍珍妮和我认识。
[误] On a dance she introduced Jane to me.

[正] At a dance she introduced Jane to me.
[注] dance 前面须用介词 at；party（聚会），reception（宴会，招待会）也用介词 at，如：He has a large circle of friends and is very popular at parties. 他交游甚广，聚会时很受欢迎。/His friend asked him to make a speech at a wedding reception. 他的朋友要求他在结婚庆典上发言。