As there are more and more serious floods in the United States, people there are paying more attention to floods.

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 space suits needn't worry about radiation damage

A．it protects him against the harmful rays from space
B．it provides sufficient light for plant growth
C．it supplies the heat necessary for human survival
D．it screens off the falling meteors