He will now retrain to fly the bigger Boeing 737s as the old planes are being phased out of service.
2018年12月四級真題（第二套）聽力 Section A
That is because the engineers, designers, regulators, operators, and all of the other skilled people needed for the new energy industry are specialists who have to be trained first ( ' , or retrained, if they are the ones being laid off in some related industry), and education, like any other complicated endeavor, takes times.