液压卡紧现象
参考答案:
当液体流经圆锥环形间隙时,若阀芯在阀体孔内出现偏心,阀芯可能受到一个液压侧向力的作用。当液压侧向力足够大时,阀芯将紧贴在阀孔壁面上,产生卡紧现象。
33.Before she______thethe door, she____what had happened to her computer.
A.walked;noticed
B.walked; had noticed
C.walks; has noticed
D.had walked; noticed
提供商业信用的债权人,为保证自己对债务的索取权而掌握的一种书面债权凭证被称为______。