When crossing a front isobars tend to ().
A. Change from smooth curves within the air mass to sharp bends at the front
B. Change from sharp bends within the air mass to smooth curves at the front
C. Pass smoothly across the front with no change
D. Become closer together at the front and pass through in straight lines
哪项是门静脉高压的声像图表现
A. 门静脉内等回声团，其与管壁间血流变细，局部门静脉管壁规整清晰
B. 门静脉内稍强回声团，门静脉管壁残缺或不清楚
C. 门静脉主干为条索样强回声，周围可显示网络状管道，可见门静脉血流
D. 肝实质内纺锤形或卵圆球状无回声，与门静脉相通，内可见门静脉血流
E. 门静脉内径＞13MM，脾门区脾静脉内径＞10MM
井下大巷列车运输火工品行驶速度不得超过()m/s，且不得同时运送其他物品或工具。
A. 1
B. 2
C. 3
哪项是门静脉海绵样变性的声像图表现
A. 门静脉内等回声团，其与管壁间血流变细，局部门静脉管壁规整清晰
B. 门静脉内稍强回声团，门静脉管壁残缺或不清楚
C. 门静脉主干为条索样强回声，周围可显示网络状管道，可见门静脉血流
D. 肝实质内纺锤形或卵圆球状无回声，与门静脉相通，内可见门静脉血流
E. 门静脉内径＞13MM，脾门区脾静脉内径＞10MM
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