[单项选择]

Radiation Effect

Space is a dangerous place, not only because of meteors (流星)but also because of rays from the sun and other stars. The atmosphere again acts as our protective blanket on earth light, gets through, and this is essential for plants to make the food that we eat. Heat, too, makes our environment endurable. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are exposed to this radiation, but their spacesuits or the walls of their spacecrafts, if they are inside, do prevent a lot of radiation damage.
Radiation is the greatest known danger to explorers in space. The unit of radiation is called "rem" (“雷姆”). Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged, the figure of 60 reins has been agreed on. The trouble is that it is extremely difficult
A. the Apollo mission was very successful
B. protection from space radiation is no easy job
C. astronauts will have deformed children or grandchildren
D. radiation is not a threat to well-protected space explorers