Learn Finnish: Tämä on vaativin simulaatio, sillä se testaa kaiken. - This is the most demanding simulation, for it tests everything.

First, we create the present active participle by adding -va to the strong vowel stem of vaatia (to demand), giving us vaativa (demanding). To make it superlative (the most demanding), we take that stem, drop the final vowel -a, and add the superlative suffix -in, resulting in vaativin.

If we needed to use vaativin in a different case or the plural, what stem would we use?

The superlative ending -in changes to -impa- (strong) or -imma- (weak) before case endings, following standard consonant gradation. For example, if the noun were plural, you would say vaativimmat simulaatiot. Superlative participles inflect exactly like regular superlative adjectives.

Why does the sentence use sillä instead of koska?

Both words mean because or for, but sillä is a coordinating conjunction while koska is a subordinating conjunction. The main practical difference is that sillä cannot be used to start a sentence, whereas koska can. Using sillä here gives a slightly more formal, explanatory tone, much like using for instead of because in English.

Why is the word for everything written as kaiken instead of the nominative kaikki?