I am no physicist, but I imagine you have all blown air over the top of an empty bottle and heard the sound it makes.

我不是物理学家，但我想你们都曾往一个空瓶子的顶部吹过气，并听到过它发出的声音。

youdao

I found an empty notebook, opened it up to the first page-and only then did I open my mouth and speak those words into the air, letting them free.

我找来一本空白笔记本，翻开第一页——这时我才张口说话，让言语在空气中自由。

youdao

I found an empty notebook, opened it up to the first page-and only then did I open my mouth and speak those words into the air, letting them free.

我找来一本空白笔记本，翻开第一页——这时我才张口说话，让言语在空气中自由。

youdao