[问答题] 试述油井结蜡的危害。

破碎 You are creating a Windows Forms application by using the .NET Framework 3.5. You create a new form in your application.You add a PrintDocument control named pntDoc to the form.To support the print functionality， you write the following code segment in the application  （Line numbers are included for reference only.） You need to ensure that the following requirements are met：  （1）When the user has no print access， font and file stream initializations are not executed and the print operation is cancelled   （2）Print operations are logged whether or not the user has print access    What should you do？（） ["A","B","C","D"] 全身制动时，观察约束肢体末梢循环情况的时间间隔应小于：（） ["10min","15min","20min","30min","45mi"] LOAEL指的是（） ["未观察到有害作用水平","观察到有害作用的最低水平","观察到作用的最低水平","阈值"] 离合器上安装扭转减振器是为了防止（） ["曲轴共振","传动系共振","离合器共振"] 试述油井结蜡的危害。