一均质杆AB重W=30N，长100cm被悬于竖直的两墙之间，不计摩擦，则墙面的反力为

加速器有些部位为防止在强电场下放电，需充适量绝缘气体，请在下列气体中选出目前最常用的气体()

A．氮气 

B．6氟化硫 

C．空气 

D．氟里昂 

E．氦气

The _____ famous family of musicians were the Strauss family.[ ]

A. more

B. most

C. much

图（一）表示呼吸过程中（　　） 时的状态，此时呼吸肌的运动状态是：肋间肌（　　），膈肌（　　）

A．吸气、收缩、收缩

B．吸气、舒张、舒张

C．呼气、舒张、舒张

D．呼气、收缩、收缩

一质量为2千克的物体，在10牛拉力作用下沿水平地面前进了1米，在此过程中，试求：

（1）拉力所做的功．

（2）物体重力所做的功．

British cancer’ researchers have found that childhood leukaemia is caused by an infection and clusters of cases around industrial sites are the result of population mixing that increases exposure. The research published in the British Journal of Cancer backs up a 1988 theory that some as yet unidentified infection caused leukaemia--not the environmental factors widely blamed for the disease.

"Childhood leukaemia appears to be an unusual result of a common infection," said Sir Richard Doll, an internationally-known cancer expert who first linked tobacco with lung cancer in 1950. "A virus is the most likely explanation. You would get an increased risk of it if you Suddenly put a lot of people from large towns in a rural area, where you might have people who had not been exposed to the infection. " Doll was commenting on the new findings by researchers at Newcastle University, which focused on a cluster of leukaemia cases around the Sellafield nuclear reprocessing plant in Cumbria in northern England. Scientists have been trying to establish why there was more leukaemia in children around the Sellafield area, but have failed to establish a link with radiation or pollution. The Newcastle University research by Heather Dickinson and Louise Parker showed the cluster of cases could have been predicted because of the amount of population mixing going on in the area, as large numbers of construction workers and nuclear staff moved into a rural setting. "Our study shows that population mixing can account for the (Sellafield) leukaemia cluster and that all children, whether their parents are incomers or locals, are at a higher risk if they are born in an area of high population mixing," Dickinson said in a statement issued by the Cancer Research Campaign, which publishes the British Journal of Cancer.

Their paper adds crucial weight to the 1988 theory put forward by Leo Kinlen, a cancer epidemiologist at Oxford University, who said that exposure to a common unidentified infection through population mixing resulted in the disease.

Cancer Research Campaign is most possibly a（）

A. medical journal

B.research institute

C. private company

D. governmental agency