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 motorcycles moped ridership saw a resurgence. Sales of motorcycles and scooters declined 43.2% in 2009, and continued to decrease in the first quarter of 2010, with scooter sales doing worst, down 13.3% compared to a 4.6% drop for all two-wheelers. Other types of small motorcycles include the monkey bike, Welbike, and minibike. There are various types of off-road motorcycles, also known as dirt bikes, specially designed for off-road events. The term off-road refers to driving surfaces that are not conventionally paved. These are rough surfaces, often created naturally, such as sand, gravel, a river, mud or snow. These types of terrain