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 __1__ our protective blanket on earth. Light gets through, and this is essential __2__ plants to make the food which we eat. Heat, __3__ , makes our environments tolerable and some ultraviolet rays (紫外線的) penetrate the atmosphere. Cosmic (宇宙的) rays of various kinds come __4__ the air from outer space, but a great quantity of radiation from the sun are screened off. __5__ men leave the atmosphere they are exposed to this radiation; but their spacesuits or the walls of their spacecraft, if they are inside, __6__ prevent a lot of radiation damage. Radiation is the greatest known danger to explorers in __7__ . Doses of radiation are measured in units called “rems (雷目)”. We all __8__ radiation here on earth from the sun, from cosmic rays and from radioactive minerals. The “__9__” dose of radiation that we receive each year is about two milligrams; it __10__ according to where you live, and this is a very rough estimate.

　　1. A. for B. with C. on D. as

　　2. A. with B. from C. under D. for

　　3. A. again B. also C. besides D. too

　　4. A. across B .to C. from D. through

　　5. A. As soon as B. As well asC. As much as D. As possible as

　　6. A. get B. make C. have D. do

　　7. A. earth B. atmosphere C. space D. environment

　　8. A. receive B. accept C. bring D. catch

　　9. A. conventional B. commonC. general D. normal

　　10. A. shifts B. converts C. modifies D. varies

　　正確答案:1.D2.D3D4.D5.A6.D7.C8.A9.D10.D