According to scientists, people sneeze because ______.

A．Our internal clock mechanism doesn' t like rest, so keeping our routines is the key to good health.
B．We need longer holidays as we still feel tired after holidays.
C．There is a biological reason why people feel uncomfortable during holidays.
D．Holidays are part of our lives though we don' t actually enjoy them.

A．To explain why we feel discontented during holidays and immediately after holidays.
B．To show that holidays do harm to people' s health because we feel tired and uncomfortable.
C．To ask people to keep on working during holidays so that the body clock will not be disrupted.
D．To show the fact that people actually don' t enjoy their holidays.