 The third set of endings is used for stems that end in labials or post-alveolar sibilants ("б, в, м, п, ф, ш, щ, ч, ж," and "р").The fourth set of endings is used with verbs whose unaffixed form (no prefixes or suffixes) have the stress on the ending in the first person singular of the present tense.As well, most Class 2 verbs and those verb roots ending in a consonant plus "л" or "р" take these endings.