单项选择题
A．the Apollo mission was very successful B．protection from space radiation is no easy job C．astronauts will have deformed children of grandchildren D．radiation is not a threat to well protection space explorers
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
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 spacesuits needn't worry about radiation damage