In 和 at 的差別在哪裡？如果不好說明，請提供一些例句。

These words are super common and used everywhere, so it'd be impossible to describe all the differences.

However in general, "A in B" means A is inside B. A is smaller and located in the middle of B. "A at B" means B is a place, and A is an object that is located at B, but A is not necessarily smaller than B.

Sometimes the difference is obvious:

I am in the box: The speaker is inside the box. The box's walls surround the speaker.

I am at the box: The speaker is standing next to the box. The box's walls do not surround the speaker.

Sometimes there is barely any difference:

I am in the park: The speaker is inside the park. They are probably having a run or walking their dog.

I am at the park: The speaker is located at the park. They might be in the park, but they could also be waiting for a friend at the entrance of the park.