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【单选题】
如果一个信息系统，主要对象为涉及国家安全、社会秩序和公共利益的重要信息系统，其业务信息安全性或业务服务保证性受到破坏后，会对国家安全、社会秩序和公共利益造成严重损害;本级系统依照国家管理规范和技术标准进行自主保护，信息安全监管职能部门对其进行强制监督、检查。这应当属于等级保护的____。A.
强制保护级
B.
监督保护级
C.
指导保护级
D.
自主保护级
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【单选题】Which is NOT correct about business letter?
A.
There are certain rules you have to follow when drafting a business letter.
B.
Inquiry, recommendation or application letter all belong to the category of business letter.
C.
We write a business letter when we need to buy or sell something.
D.
A business letter is an official correspondence between two or more parties.
【单选题】Which is NOT correct about business letter?
A.
A business letter is an official correspondence between two or more parties.
B.
Inquiry, recommendation or application letter all belong to the category of business letter.
C.
We write a business letter when we need to buy or sell something.
D.
There are certain rules you have to follow w hen drafting a business letter.
【单选题】Which is NOT correct about business letter?
A.
Inquiry, recommendation or application letter all belong to the category of business letter.
B.
A business letter is an official correspondence between two or more parties.
C.
We write a business letter when we need to buy or sell something.
D.
There are certain rules you have to follow when drafting a business letter.
【简答题】．[实验化学] 苯亚甲基苯乙酮俗称查尔酮，淡黄色棱状晶体，熔点58℃，沸点208℃（3.3kPa）易溶于醚、氯仿和苯，微溶于醇。制备原理如下： (查尔酮) （1）制备过程中，需在搅拌下滴加苯甲醛，并控制滴加速度使反应温度维持在25～30℃，说明该反应是 （填放热或吸热）反应。如温度过高时，则可以采取 措施。 （2）产品结晶前，可以加入几粒成品的查尔酮，其作用是 。 （3）结晶完全后，需抽滤收集产物...
【简答题】在苯亚甲基苯乙酮的制备中,采用苯甲醛和( )发生羟醛缩合反应。
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