The invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene comprising contacting 1,1,1-trifluoro-2,3-difluoropropane with hydrogen fluoride in the presence of a zincchromia catalyst to produce a compound having the formula CF3CHFCH2X, wherein X is Cl or F, and dehydrohalogenating the compound of formula CF3CHFCH2X to produce 1234yf. The polarization-rotation angle of the array can be finely adjusted and maintained, even when the magnetic fields are not continuously supplied to the Faraday rotators. The end face of each engagement portion is provided with a recess at which the tape drawing mechanism chucks the leader pin. The operation then increases a weight applied to the first concept when analyzing the candidate answer and the item of supporting evidence to generate the response to the first case when the concept score exceeds a predefined maximum weight threshold.