obligatoryadj.强制性的；义务的；必须的obligatory provision强制性规定obligatory inclusion必需性包含obligatory reflector强制性反光体obligatory insurance强制保险obligatory amblyopia废用性弱视obligatory mutualism义务性共生obligatory rear lamp强制性后灯obligatory saprophyte专性死物寄生菌obligatory parasitism专性寄生obligatory water loss被动性失水