题目

Space is 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 which we eat. Heat, too, makes our environment endurable. Various kinds of rays come through the air from outer space, but enormous quantities of radiation（辐射） 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 spacecraft, if they are inside, do在某扇形统计图中，其中某一部分扇形面积所对的圆心角是45°，那么它所代表的部分占总体的A.B.C.D.