D.ug/kg

145.The half-life of radon is 4 days.After 8 days,what is the residual amount of radon?

A.1/2

B.1/4(正确答案)

C.1/8

D.1/16

146.Carbon dioxide fire extinguishers are mainly used to put out the initial fire of.

A.expensive equipment and files

B.instruments and meters,electrical equipment under 600 volts

C.oil.

D.all above(正确答案)

147.The maximum allowable temperature of using a constant temperature incubator is℃.

A.60(正确答案)

B.100

C.45

D.80

148.28.take into account the risk of electric shock.

A.36

B.65

C.25(正确答案)

149.When used properly,chemical fume hoods protect you from:

A.Chemical splashes,so you don’t have to wear eye protection.

B.Hazardous fumes or vapors.(正确答案)

C.Fire.

D.Loud noises.

150.Teachers and students who enter the laboratory to work should strictly obey the laboratory operating rules,and turn off（）,lock the doors and windows before leaving the laboratory after finishing the experiment,to prevent fire and explosion,overflow and other accidents.

A、the instruments and equipment

B、the water source,power source,air source(正确答案)

C、Computers