搜题请搜索小程序“爱下问搜题”
问题 多项选择题

以下关于隧道支护和衬砌的说明，正确的是()?

A..支护施作后即成为永久承载结构的一部分

B..支护是解决隧道稳定和安全的工程措施

C..二次衬砌应采用先墙后拱的施工顺序

D..整体移动式衬砌台车的生产能力大，施工速度快。

答案

参考答案：A, C, D

单项选择题

(五)


Space travel is definitely bad for astronauts’ bones, reducing their bone density after only a month of weightlessness, according to French research published on Friday.
Laurence Vico and his fellow workers at St Etienne University called for more research into the effects of microgravity, after their study of 15 astronauts from the Russian MIR station showed bone loss continued throughout space flights.
"Bone loss was especially striking in four astronauts, " the scientists reported in the Lancet Medical Journal.
They measured the Bone Mineral Density(BMD) of bones in the forearm and lower leg of the astronauts who had spent one to six months in space.
The BMD loss was significant in the tibia of the lower leg, a weight-bearing bone, but barely changed in the radius of the forearm. "Our results indicate the need to investigate not only different bones, but also different areas of the same bone since not all sites of the skeleton are similarly affected by space conditions, " they added.
Without gravity the body isn’t bearing any weight so there is no need for calcium which makes bones p, and it becomes empty into the bloodstream.
The research team suggested in future scientists should try to determine if the loss of bone density was only on weight-bearing bones on longer flights, also the possible recovery after returning to Earth.

Scientists have found that ______ .

A．the BMD loss may cause serious illness to astronauts

B．the BMI) loss may cause some change in astronauts’ bodies

C．astronauts shouldn’t care about the BMD loss

D．astronauts should take some calcium before space travel
查看答案
名词解释

压缩比
查看答案