waswere后是否加动词ing

题目

waswere后是否加动词ing
在They are doing some shopping at the moment.（用a moment ago 改写句子）.我无法确定are改成were后,doing是不变,还是变do.请大家集思广益,

答案

a moment ago是刚才的意思
改为they were doing some shopping a moment ago.
变成过去进行时,表示过去某个时刻正在进行的动作或状态：他们刚才正在购物.