设备或电路发生障碍后，在较短时间内自行恢复，而障碍原因不明称为设备和电路障碍。

项目进度控制总目标按年、季、月计划分解为()。

A．时间分目标

B．完工分目标

C．交工分目标

D．竣工分目标

（）是企业安全生产的运作保障机制，是企业安全精神文化的外化表现，是企业安全行为文化的规范和准则，是实现企业安全物质文化的依据。

A.企业安全物质文化

B.企业安全制度文化

C.企业安全价值规范文化

D.企业安全精神文化

下列有关人类遗传病的叙述，正确的是（）

A.先天性疾病都是遗传病

B.遗传病一定是先天性疾病

C.遗传病是指由遗传物质改变而引起的疾病

D.遗传病都是由基因突变引起的

Brian arrived at San Francisco airport two hours before the flight to Paris. He was wearing three shirts, a jacket, two pairs of socks, a pair of shorts, and two pairs of jeans. He was carrying one small backpack, which was very full, but he didn’t have any other luggage. Brian needed to meet a man named Tony before he checked in for his flight. He found Tony near the Air France counter. Tony gave him a round trip ticket and a small package.

"Give this package to Jean Paul at the airport in Paris. He will have a sign with your name on it. I think you can find him easily," Tony said," You don’t have any luggage, right"

"Only this backpack," Brian answered. "You said I could bring one carry on bag. "

"That’s right. One carry on bag is fine. Have a good trip. "

"Thanks. "

Is Brian a criminal Not at all. He is an air courier. And he paid only $110 for the round trip ticket to Paris. Air couriers get cheap airline tickets because they take important packages and papers to foreign countries. Businesses sometimes need to get packages and papers to people in foreign countries by the next day. Often, the only way they can do this is to use an air courier company. It is not cheap for a business to send a package with an air courier, but it is quick.

Every year about 80,000 people worldwide travel as air couriers. The number of tickets for courier travel is growing by about 10 percent a year. However, air courier travel isn’t for everyone. But if you have very little money, can be flexible about your travel plans, and don’t mind wearing the same clothes for a week, it can be a great way to take a vacation!

Business choose the air courier service because （）.

A．it costs less

B．it is flexible

C．it saves time

D．it grows fast

若井壁取心泥饼太厚，可能是钻井液失水量过大造成，不需重新取心。（）