问题
多项选择题
超声成像的一般规律有（）.
A.回声不仅来自大界面的反射，也有散射回声
B.物体衰减大小表现在后方回声的强弱
C.囊性物体声像图特点是内部无回声，前、后壁回声增强，侧壁呈侧声影，后方有回声增强
D.多重回声反射表现为一系列间隔均匀，依次减弱的影像
E.采用非线性检测可获得二次谐波成像
答案
参考答案：A, B, C, D, E
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超声成像的一般规律有（）.
A.回声不仅来自大界面的反射，也有散射回声
B.物体衰减大小表现在后方回声的强弱
C.囊性物体声像图特点是内部无回声，前、后壁回声增强，侧壁呈侧声影，后方有回声增强
D.多重回声反射表现为一系列间隔均匀，依次减弱的影像
E.采用非线性检测可获得二次谐波成像
参考答案：A, B, C, D, E
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| Earthquakes are 1 ; thousands of them happen each day. But most are too weak to feel. During a big earthquake. there is often a great noise first. Then the earth 2 terribly; many houses fall down. Railway tracks break and trains go 3 lines; a great many factories are 4 ; thousands of deaths are caused, and many more lose homes... 5 the great damage and deaths caused by the earthquake itself, other disasters such as fires often 6 . More buildings are destroyed and more 7 are caused. It is well known of the 8 of a possible earthquake, and for centuries man has been making researches on earthquakes. More than 2,000 years ago, 9 , a Chinese scientist named Zhang Heng invented a machine which could find out from which 10 the seismic (地震的) waves had come, and this machine is still 11 by scientists today. Now we know much more about earthquakes and 12 they happen, but we still cannot tell exactly when and where an earthquake will happen, and cannot 13 it from happening. So earthquakes are among the 14 disasters in the world. No one can stop natural earthquakes. 15 , scientists can help stop earthquakes destroying whole cities and causing too many deaths. | ||||
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