Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
Interrogative word Interrogative word An interrogative word or question word is a function word used to ask a question, such as "what", "when", "where", "who", "whom", "why", and "how". They are sometimes called wh-words, because in English most of them start with "wh-" (compare Five Ws). They may be used in both direct questions ("Where is he going?") and in indirect questions ("I wonder where he is going"). In English and various other languages the same forms are also used as relative pronouns in certain relative clauses ("The country where he was born") and certain adverb clauses ("I go where he goes").