* Verb (present participle): This is the most common usage. It describes an action in progress, like "The bridge is extending across the river."
* Adjective: Describing something that is long or that stretches out, like "The extending arm of the crane reached the top floor."
* Noun: This is less common, but it can refer to the act of extending something, like "The extending of the deadline was a relief."
To determine the part of speech, you need to analyze the sentence it's used in.