One reason for the difference between the British people working abroad and the average person at home is that the former ______.

A．to warn the readers against misunderstanding the British people
B．to make a brief introduction to different social classes in Britain
C．to criticize the nonsense written about Britain
D．to describe the living conditions in Britain

A．exposure to even tiny amounts of radiation is fatal
B．the effect of exposure to radiation is slow in coming
C．radiation is avoidable in space exploration
D．astronauts in spacesuit needn't worry about radiation damage