Killed vaccines consists of pathogens or fragments of pathogens that has been grown in culture and killed (so it won't have disease-producing capacity anymore). The pathogens are killed by heat or chemical methods. Those vaccines are safe, as the pathogens are inactivated and can't provoke the disease anymore. In opposition to the killed vaccines, the live vaccines consists of live pathogens that are attenuated, so they create an immune response but don't cause the disease. So, as the live vaccines are attenuated, not the killed vaccines, the correct answer is b) Those vaccines are live attenuated.