How long did Ethell teach minority students（）

A．It can measure the driver’s alcohol level in the blood.
B．It bases its analysis on the driver’s heartbeat.
C．It can quicken the driver’s response to emergencies.
D．It monitors the signals transmitted from the driver’s brain.

A．He has to read a history book.
B．He is too busy to go with her.
C．He has already visited the museum.
D．He must hand in a report about the museum.