根据我国国家标准GB17859-1999,第5级称为()
A.系统审计保护级
B.安全标记保护级
C.结构化保护级
D.访问验证保护级
参考答案:D
化学在生产和日常生活中有着重要的应用.下列说法不正确的是( )
A.明矾水解形成的Al(OH)3胶体能吸附水中悬浮物,可用于水的净化
B.在海轮外壳上镶入锌块,可减缓船体的腐蚀速率
C.MgO的熔点很高,可用于制作耐高温材料
D.电解MgCl2饱和溶液,可制得金属镁
They always do _____ every day, because they know it is _____ for them to do so. [ ]
A. enough exercise; enough easy
B. exercise enough; easy enough
C. enough exercise; easy enough
D. exercise enough; enough easy