题目

At, call, try, discover, however, beyond, travel, send, be, understand, reach， goodScientists think that there has    1    life on the earth for millions of years.    2   , we haven’t found life on other planets yet. Why? The earth is a planet and it goes around the sun. There are other planets that also go around the sun. The sun and its planets    3    the solar system(太阳系). The solar system is a small part of our galaxy(银河系). The stars we see at night are the suns in other solar systems. There are more than 200 billion stars in our galaxy, the Milky下列物质中属于氧化物的是（　　）A．干冰B．纯碱C．食醋D．花生油