同事之间礼仪应注意些什么？

在“聚乙烯、淀粉、活性炭、二氧化碳、氧化铁、小苏打、汞”中选择适当的物质填空：

（1）可作气体肥料的是______；（2）可作热塑性材料的是______；

（3）用于温度计的是______；（4）用于治疗胃酸过多的是______；

（5）用于防毒面具的是______；（6）大米、小麦中的主要物质是______．

阅读理解。

     The space shuttle Columbia flared and broke up in the skies over Texas on Saturday, February 1, 2003,

killing the seven astronauts on board in what NASA and President Bush called a tragedy for the entire nation.

NASA launched an investigation into the disaster and began searching for the astronauts' remains. It said that

although there had been some data failures it was too early to nail down a precise cause. The break-up, 16

minutes before the shuttle was due to land at Kennedy Space Center in Florida, spread possibly toxic debris

(有毒的残骸) over a wide area of Texas and neighboring states.

     Dramatic television images of the shuttle's descent clearly showed several white trails (痕迹) streaking

through blue skies after the shuttle suddenly fell apart. It was almost 17 years to the day that the Challenger

shuttle exploded on Jan. 28, 1986, killing all seven astronauts on board.

     Take-off and re-entry into Earth's atmosphere are the most dangerous parts of a space mission. In 42

years of US' human space flight, there had never been an accident in the descent to Earth or landing.

Challenger exploded just after take-off.

     Rescue teams scrambled to search for the remains of the crew, which included the first Israeli to fly on

the shuttle, former combat pilot Col. Ilan Ramon. There were warnings that parts of a vast 120-mile-long

corridor of debris could be toxic because of poisonous rocket propellant (推进器).

     "We are not ready to confirm that we have found any human remains," Nacogdoches County Sheriff

Thomas Kerrs said. He added that among the roughly 1,000 calls reporting debris, some people said they

found remains of crew members.

     "The Columbia is lost. There are no survivors, …Their mission was almost complete and we lost them

so close to home. … America's space program will go on," said a grim-faced Bush in a message broadcast

on television, which included condolences (同情) to the families of the dead astronauts. 

1. The word "descent" in the passage means _______.

A. taking off

B. landing

C. orbiting (绕轨运行)

D. walking down

2. Which is true of the Israeli astronaut Ilan Ramon?

A. He was the first Israeli astronaut to fly on the shuttle.

B. He was the first foreign astronaut to fly on the American shuttle.

C. He used to be a passenger plane pilot.

D. He was the only survivor in the Columbia disaster.

3. The Columbia disaster and the Challenger disaster were similar in that _______.

A. there were seven astronauts killed on board

B. both the shuttles exploded when they took off

C. Both the shuttles exploded when they were about to land

D. no human remains were found

4. Which of the following is wrong according to the news?

A. The U.S.A. will give up the space program because of the accident.

B. NASA hasn't found the cause of the Columbia disaster.

C. Before the Columbia disaster, no shuttles had exploded in the course of landing.

D. Take-off and re-entry into Earth's atmosphere are the most dangerous parts of a space mission.

为胚胎在受体内的存活提供了可能的原因有（）

①同种动物的供体、受体生殖器官的生理变化是相同的

②早期胚胎在母体子宫内处于游离状态

③供体胚胎可与受体子宫建立正常生理和组织联系

④受体对移入子宫的外来胚胎基本上不发生免疫排斥反应

A.①③④

B.②③④

C.①②③

D.①②③④

井字架是施工中最常用的（）运输设备

A、水平

B、倾斜

C、垂直