When he was little I helped him with math problems once.

当他还是个小孩子的时候，我有一次曾经帮他做数学题。

youdao

Once I recognized the feeling of my baby's little flips, I savored those private moments between the two of us, especially when I was feeling annoyed at work or in meetings.

我一识别到婴儿轻微的击打就跟它一起享受这种私人的时刻，特别是在我工作或会议期间感到烦恼的时候。

youdao

Once I had a little dog who used to look at me with sad eyes when I coughed: he was the only living creature I have ever loved.

我要告诉你一个笑话：从前我有一只小狗，当我咳嗽的时候，它总是用悲哀的神气瞅着我，它是我唯一喜爱过的动物。

youdao

And when I threw those away, I was left once again with a little box, and I could do it again, and again, and again.

剔除之后,我得到了更小的方格,我可以一次一次的重复这个过程

耶鲁公开课 - 博弈论课程节选

Once when I was a little boy I received as a gift a toy cement mixer.

NEWYORKER: All That