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
French articles and determiners French indefinite article is analogous to the English indefinite article "a/an". Like "a/an", the French indefinite article is used with a noun referring to a non-specific item, or to a specific item when the speaker and audience do not both know what the item is; so, « J'ai cassé une chaise rouge » ("I broke a red chair"). Unlike "a/an", the French indefinite article has a plural form, often translated as "some" but usually simply omitted in English; so, « Il y a des livres là-bas » ("There are some books over there" or "There are books over there"). The