What part of speech is ring?

"Ring" can be several parts of speech depending on how it's used in a sentence. Here are a few examples:

Noun: A piece of jewelry worn on a finger.

* "She gave him a diamond ring."

Verb: To make a sound like a bell.

* "The phone rang."

Verb: To surround or encircle.

* "The city rings the lake."

Adjective: Shaped like a ring.

* "The tree has a ring of leaves around the trunk."

Interjection: Used to express surprise or alarm.

* "Ring! Someone's at the door!"

Without more context, it's difficult to determine the specific part of speech "ring" is acting as.