The word "significant" in Paragraph 3 has the similar meaning with ______.

A．affect the healthy growth of our offspring
B．damage cells which may grow into cancer years later
C．kill large numbers of cells in main organs so as to cause death immediately
D．all of the above

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.