Vowel whose quality does not change over the duration of the vowel is called a monophthong. Monophthongs are sometimes called "pure" or "stable" vowels. A vowel sound that glides from one quality to another is called a diphthong, and a vowel sound that glides successively through three qualities is a triphthong. All languages have monophthongs and many languages have diphthongs, but triphthongs or vowel sounds with even more target qualities are relatively rare cross-linguistically. English has all three types: the vowel sound in "hit" is a monophthong , the vowel sound in "boy" is in most dialects a diphthong , and
Types of inhabited localities in Russia they are all still largely based on the system used in the RSFSR. In all federal subjects, the inhabited localities are classified into two major categories: urban and rural. Further divisions of these categories vary slightly from one federal subject to another, but they all follow common trends described below. In 1957, the procedures for categorizing urban-type settlements were further refined. Multiple types of rural localities exist, some common through the whole territory of Russia, some specific to certain federal subjects. The most common types include: Types of inhabited localities in Russia The classification system of the types of inhabited