According to the passage, if an air plane has an accident-free record, it usually pays to the insurance company ______.

A．Emphasizing the importance of protection from radiation.
B．Solving the mystery about radiation.
C．Discussing the cause of cancer.
D．Introducing the nuclear power.

A．We can't detect radioactivity even with modern equipment.
B．Only radiation at very high levels can kill an animal or human being.
C．If a few cells are only damaged, healthy cells will take the place of dead ones.
D．Radiation is harmful no matter what level it is.