"Are they washing the dog?"
Translation:Pesevätkö he koiraa?
I am not a native speaker but:
In Finnish there exists something called vowel harmony. Each word (except for some compound words or words from other languages) can be put in one of the following two categories: - Words with a, e, i, o, u - Words with ä, e, i, ö, y
Words that only contain e or i belong to the category with ä, e, i, ö, y.
When adding affixes you always have to add the one with the corresponding vowel harmony.
Beware that for some words like minä the stem is minu, which leads to the adessive form minulla and not minullä, even if minä per se would belong to the other category