问题
单项选择题
垂直线性良好的超声波探伤仪，用0°探头发现同一对比试块上的某一平底孔回波，比同声程处φ3mm平底孔回波高5dB，则该平底孔约为（）。
A、φ4mm
B、φ5mm
C、φ5．5mm
D、φ8mm
答案
参考答案：A
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垂直线性良好的超声波探伤仪，用0°探头发现同一对比试块上的某一平底孔回波，比同声程处φ3mm平底孔回波高5dB，则该平底孔约为（）。
A、φ4mm
B、φ5mm
C、φ5．5mm
D、φ8mm
参考答案：A
We know 1 about the universe(宇宙). It means the earth, the sun, the moon, the stars, and the space 2 them. Most of the stars are much 3 than the moon, but they look smaller 4 they are far away from the earth. At night, the moon is high in the sky 5 a light. But the moon has 6 light of its own. The light of the moon comes from the sun. The sun gives us light, heat and life. And the plants, animals and men will die 7 the sun. The earth goes around itself 8 . When the part of the earth 9 to the sun, it is day. The 10 part of the earth is night. The earth is our homeland. We should love it.
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