After a period of time, people started to recognize that one significant problem was round-tripping.

经过一段时间之后，人们开始认识到其中一个显著问题是往返旅程。

youdao

After a period of time, people started to recognize that one significant problem was round-tripping.

经过一段时间之后，人们开始认识到其中一个显著问题是往返旅程。

youdao