A beam of light will not bend round the corners unless ______ to do so with the help of a reflecting device.

A．its intelligence and cost are beyond question
B．it is able to bear the rough environment
C．it is made as complex as the human brain
D．its architecture is different from that of the present ones

A．the greenhouse effect
B．the burning of fossil fuels
C．the potential effect of air pollution
D．the likelihood of a new ice age