什么叫缓蚀剂?常用的有哪几类?简要叙述各类缓蚀剂的防蚀原理和特点。
A crew member reports that the high-pressure alarm light of a low-pressure CO2 fixed fire extinguishing system is illuminated. The most probable cause of this condition would be that().
A. an air leak has developed in the tank
B. the tank cooling system has malfunctioned
C. the pilot cylinder discharge valve is leaking
D. an excessive amount of insulation has been installed on the tank and piping
2012年末某市人口数为20万人,零售商业机构600个,以下表述正确的是()。
A. 零售商业网密度属于强度相对指标
B. 600个/200千人,说明该市居民每千人中有3个零售网点为他们服务
C. 200000人/600个,说明每333人拥有一个零售网点
D. 零售商业网密度采用的是复名数
E. 零售商业网密度可以计算正指标和逆指标
对于弥漫性轴索损伤中微小脑挫伤灶及早期脑梗死的显示,常需进行()。
A. CT平扫
B. CT增强扫描
C. MRI
D. PET
E. SPECT