grammatical number - The last few years "has seen" vs "have seen"?

Consider the following sentences:

The last few years has seen the building of the new church.

and

The last few years have seen the building of the new church.

As a native speaker, both of these sentences "sound" correct to me. Is only one of them correct, are they both correct or is each one only correct in specific circumstances.

This was a question one of my students asked me, so if there is a relevant grammar rule, that would be great.

Answer

Years, being plural, takes the plural form have. But the last few years, being a single span of time, takes the singular form, has.

That's why they both sound okay to you. The first option is generally preferred in formal writing.