Did you remember to return the digital camera to Sarah?

题目

Did you remember to return the digital camera to Sarah?
Yes,I gave it to her ____I saw her.
A the moment B once
once 为什么不可以解释一但啊 我一但看到他就给他 貌似也可以的 那Once 与 the moment 区别在那呢

答案

我一旦看到他就给他,事实上还没给他
gave说明已经给了,所以用the moment