120阀设计成二级控制,当衽紧急制动,即列车主管紧急排风减压时,在紧急阀中先比较容易

题型:单项选择题

问题:

120阀设计成二级控制,当衽紧急制动,即列车主管紧急排风减压时,在紧急阀中先比较容易地打开一个尺寸较少的先导阀,消除大尺寸的紧急放风阀背压,紧接着再顶开放风阀,这一连串动作在一瞬间完成,消除了103阀在紧急活塞杆顶到放风阀时所停留的时间,这样就缩短了列车主管热电厂风过程,大大提高了紧急制动()

A.波速

B.作用

C.效果

D.功能

考点:机车车辆管道工机车车辆管道工(高级)机车车辆管道工(高级)题库
题型:单项选择题

Most animals protect(保护) their young until they are old enough to take care of themselves. A fish that swims in the rivers of South America protects its young in a very strange way. This fish, a kind of catfish, uses its mouth to keep its babies from danger(危险).

When this catfish lays(产卵) its eggs, it carries them in its mouth. From what we know, it does not eat during this time. After the eggs hatch(孵化), the fish swims with its young to protect them. It opens its mouth when danger appears(出现), and the tiny fish swim inside. They swim out only when it’s safe again.

These catfish may have a peculiar way to protect their young, but it seems(好像) to work.

小题1:The best title(标题) is _____________.

A.Staying Away From Danger

B.How A Fish Protect Its Young

C.Laying Eggs

D.A Cat That Swims小题2: The catfish in the story live in _________________.

A.lakes

B.the sea

C.rivers

D.North America小题3:The young fish are ____________________.

A.tiny

B.large

C.yellow and gold

D.very brave小题4:If the young fish were not near their parents, they would be ______________.

A.safer

B.in greater danger

C.happier

D.less hungry小题5: The word “peculiar” in the story means ________________.

A.easy

B.useless

C.strange

D.dangerous

题型:单项选择题

急性化脓性根尖周炎理想的排脓方式()

A.穿通骨壁突破黏膜

B.穿通骨壁突破皮肤

C.通过根尖孔经根管从冠部排脓

D.通过牙周膜从龈沟或牙周袋排脓

E.以上均不是

题型:单项选择题

烤烟采用地膜覆盖栽培的作用不包括下列()项。

A.减轻杂草和病虫危害

B.增温保墒

C.减少养分流失

D.降低叶片厚度和烟碱含量

题型:单项选择题

行为科学51、英国现代教育制度确立的标志是1944年颁布的()

题型:单项选择题

尿毒症肾性骨营养不良早期诊断依据是()

A.骨活检

B.骨骼X线检查

C.骨痛症状

D.血钙、磷水平

E.肾功能检查

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