在实验室里，我们需要小心处理乙醚，因为它极易挥发和燃烧。

In the lab, we need to handle ___ether carefully because it's highly volatile and flammable.

鸟儿飞向高空，消失在苍穹之中。

The birds soared high and vanished into the ___ether.

19世纪的科学家们认为光是通过以太传播的。

Scientists in the 19th century believed light traveled through the ___ether.