In the second paragraph, "the third "means ______.

A．Automation helps solve the problem of working at night.
B．A person can work more efficiently by frequent changes between day shifts and night shifts.
C．The adaptation to night work can be destroyed if the persons revert to their normal habits for even one day or two.
D．Those permanent night workers are more likely to have such symptoms as digestive disorder.

A．It involves the use of a deadly poison.
B．It is a costly event which rarely occurs.
C．The hunters have set rules to follow.
D．The hunters have to go through strict training.