How should you combine the prefix 'un' with the word 'natural'?

The correct formation combining the prefix 'un' with the word 'natural' is "unnatural." The prefix 'un-' is used to create an antonym or negate the meaning of the base word, in this case, 'natural,' which means something that is inherent or typical to nature. By adding 'un-' to 'natural,' you denote something that is not natural, such as artificial or synthetic.

In English, when the prefix 'un-' precedes a word that starts with a consonant, there is no need to alter the spelling of either the prefix or the base word. This principle ensures readability and maintains the integrity of the original word. Therefore, 'natural' remains intact, with the prefix simply added at the beginning, resulting in 'unnatural.'

Other options presented do not adhere to standard English spelling rules, either omitting letters or introducing unnecessary variations, which can confuse meaning and clarity.