∵直线a∥b，直线b∥c，∴直线a∥b∥c，∵∠1=45°，∠2=100°，∴∠ABE=∠1=45°，∠EBC=∠BMF=180°-∠2=80°，∴∠ABC=∠ABE+∠EBC=45°+80°=125°，故选A．
