There used to be a lot of pandas 怎样改为反意疑问句

问题描述:

There used to be a lot of pandas 怎样改为反意疑问句
反意疑问句应该是在句子加个逗号 的那种吧

陈述部分的谓语是used to 时,疑问部分用didn't +主语或 usedn't +主语.
Didn't there used to be a lot of pandas.
Usedn't there to be a lot of pandas.