上门服务人员应在预约时间前（）到达现场，若因特殊原因确实需要改变上门服务时间的，应至

管道系统实验前，应与运行中的管道设置隔离盲板，对水或蒸汽管道如果以阀门隔离时，阀门两侧温差不得超过（）。

A、50℃

B、100℃

C、150℃

D、200℃

单体液压支柱初撑力不可以低于（）

Six years later, in an about-face, the FBI admits that federal agents fired tear gas canisters capable of causing a fire at the Branch Davidian compound near Waco, Texas in 1993. But the official said the firing came several hours before the structure burst into flames, killing 80 people including the Davidians’ leader, David Koresh.

"In looking into this, we’ve come across information that shows some canisters that can be deemed pyrotechnic in nature were fired--hours before the fire started," the official said. "Devices were fired at the bunker, not at the main structure where the Davidians were camped out."

The Federal Bureau of Investigation maintains it did not start what turned to be a series of fiery bursts of flames that ended a 51-day standoff between branch members and the federal government. "This doesn’t change the bottom line that David Koresh started the fire and the government did not," the official said. "It simply Shows that devices that could probably be flammable were used in the early morning hours."

The law enforcement official said the canisters were fired not at the main structure where the Davidian members were camped out but at the nearby underground bunker. They bounced off the bunker’s concrete roof and landed in an open field well, the official said. The canisters were fired at around 6 a.m. , and the fire that destroyed the wooden compound started around noon, the official said. The official also added that other tear gas canisters used by agent that day were not flammable or potentially explosive.

While Coulson denied the grenades played a role in starting the fire, his statement marked the first time that any U.S. government official has publicly contradicted the government’s position that federal agents used nothing on the final day of the siege at Waco that could have sparked the fire that engulfed the compound. The cause of the fiery end is a major focus of an ongoing inquiry by the Texas Rangers into the Waco siege.

After reading the passage, how much do you know about the compound near Waco（）

A. About 51 people lived in the compound at the time of the event in 1993

B. It consisted of a main structure and a bunker

C. It was built of stone

D. It was a schoolhouse

井上下必须设置消防材料库。

输送液化天然气介质的管线上安装的阀门应为（）。

A、常温阀门

B、耐热阀门

C、低温阀门

D、超低温阀门