A physically and mentally active
B be alert and receptive
C engage in mental, activities
D the benefits of challenging the brain
E beneficial and happy
F maintain mental alertness
Older people need to keep both_______.

A．Radars that can help drivers to see obstacles in fog.
B．Devices that can help drivers to see through big vehicles.
C．Improvements in seat belts, pedal controls and tyres.
D．Windscreens that can help drivers to improve their vision.