Derailleur gears several standards in use, and in each the product of the derailleur's actuation ratio and the length of cable pulled must equal the pitch of the rear sprockets. The following standards exist. Some rear derailleurs, especially for mountain bikes, incorporate a clutch to keep the lower length of chain in sufficient tension to prevent the chain from striking the bottom of the chain stay, called "chain slap", and which can damage the chain stay. Clutches are also helpful in preventing the chain from derailing from the chain ring on systems without a front derailleur. The front derailleur only has to
Influence of French on English among the clergy. French was therefore, at first, spoken in England under the form of this Anglo-Norman dialect. During the 12th century, continental French had a greater influence on Old English. It acquired great prestige in England, especially within the aristocracy and the clergy. It became the language of law and justice nationwide. Rich and noble families, most of them of Norman origin, taught their children French or sent them to study in France. The expansion of the French language in England was also encouraged by royal marriages. From Henry II Plantagenet and Eleanor of Aquitaine at the beginning of