Question

On a clear day, you can see Ulleongdo form Dokdo because it's only 87.4 km away.
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(-do means 'island')
What does 'it' refer to? Does 'it' refer to 'Ulleongdo'?
Or is 'it' an impersonal pronoun referring to 'the distance' as follows?

1. It is 100 meters away from here to the station.

Answer 1

In that sentence, "it" refers to Ulleongdo. Try substitution, and you'll see:

... because Ulleongdo is only 87.4 km away.

Please note that you mean "from" not "form" in that sentence!

Answer 2

Thank you for your help.

On a clear day, you can see Ulleongdo from Dokdo because it's only 87.4 km away.

Answer 3

You're very welcome!

=)