气孔减少了铸件的有效截面积，造成局部（），降低了铸件的力学性能。
参考答案：应力集中
When we _______the railway station, the train _______for 5 minutes．
A．got to, had been away
B．reached, had left
C．arrived, has been away
D．arrived at, has left
肺淤血最早出现可靠征象是______
A．肺纹理增加、模糊 B．肺水肿C．上肺静脉扩张，与下肺野血管比例改变D．胸腔积液 E．以上都不是
