泵入口水平敷设吸入管变径时，只允许安装斜面向下的（）大小头。
A、同心
B、偏轴
C、偏心
D、同轴
参考答案：C
—Can you give me some advice on listening?
—I think you'd better _______ to some English programmes every day. [ ]
A. listen
B. listened
C. listening
D. to listen
物质对X线的总衰减系数包括
A．光电衰减系数B．相干散射衰减系数C．康普顿衰减系数D．电子对效应衰减系数E．以上都是
