Tom has to be at the station before the ______.

A．Rose left teaching to work for a drug company.
B．Rose misses her friend since she got a new job.
C．Rose doesn’t know who will teach chemistry.
D．Rose’s company doesn’t have a chemist to test new drugs.

A．Teacher and student.
B．Waiter and customer.
C．Dentist and patient.
D．Parents and child,