In the first sentence of Paragraph 4," . manage this" means "to manage the process of ______ "

A．healthy people should live separately from unhealthy members of the family
B．a germ-free home is not only possible, but significant
C．unless you live with the vulnerable, it is pointless to sterilize the air
D, our immune systems are too weak to fight against the food poisoning bacteria

A．they did not receive food when they were hungry
B．they mastered their body movements too quickly
C．someone came too close to them
D．they saw an object disappear