【单选题】Why did it take the scientists a long time to locate the planets?
A.
Because there are too many of them.
B.
Because they are much dimmer than their parent stars.
C.
Because the scientists' method was wrong.
D.
Because they are moving all the time.
【单选题】目前使用的打印机,需使用硒鼓的通常是( ) 打印机.
【单选题】目前使用的打印机,需使用硒鼓的通常是()打印机。
【单选题】—I'm not sure _________there are living things on the planets or not. —Even scientists aren't sure about it. [ ]
【单选题】It is believed by most scientists that______.
A.
the moon was hit by an object as large as Mars
B.
the moon formed from pieces of rock from Mars
C.
the pieces from Mars came together to form. the earth
D.
the moon is made up of materials similar to those of the earth
【单选题】______the bones under the sand,the scientists concluded that they came from the dinosaurs about 65 million years ago.
【单选题】锯削软材料和较大平面及厚材料时应选用____锯条;锯削硬材料和管子或薄材料时应选择____锯条。正确答案是