He thought that if he couldn't see something, it didn't exist.

他认为自己看不见的事务就不存在。

Research opportunities exist in a wide range of areas.

众多领域都存在着研究机会。

animals that no longer exist.

不再存在的动物。

I was barely existing.

我勉强度日。

Some people exist on melons or coconuts for weeks at a time.

一连数周靠吃各种瓜果或椰子生存。