极限荷载
参考答案：
是指地基即将失去稳定性，，土体将要从基底被挤出时，作用于地基上的外荷载。
One of the most inportant questions they had to consider was ____ of public health. [ ]
A. that
B. this
C. that
D. which
对肺动脉高压的肺血流频谱的叙述错误的是（）
A.ACT（加速时间）缩短
B.ACT/RPEP（右室射血前期时间）比值增大
C.RPEP延长
D.RVET（射血时间）缩短
E.ACT/RVET比值变小
