空气中的硫化氢浓度达到（）g/m3时，人就会中毒。
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网优平台维护作业计划中性能数据的执行周期为周。
A. 正确
B. 错误
开松与除杂所遵循的原则是什么？为什么要遵循这个原则？
You are responsible for implementing maintenance jobs on a SQL Server 2005 database server. Certain jobs run every Sunday and other jobs run at the beginning of every month. You need to schedule the jobs in the way that uses the least amount of administrative effort. What should you do? （）
A. Create a job schedule that runs every Sunday. Assign weekly tasks to this schedule. Create a second schedule that runs on the first day of every month. Assign monthly tasks to this schedule.
B. Create a job for each task that runs once a day. Use a Transact-SQL statement to check the date and day of the week. If the day is either a Sunday or the first day of the month, execute the code.
Create a job schedule that runs once a day. Assign jobs to this job schedule. If the day is either a Sunday or the first day of the month, execute the jobs.
D. Create a job for each task that runs once a week on Sunday. Add a second job schedule that runs the job on the first of the month.
磁控管的灯丝电压一般为（），工作电流约为（），阳极峰值电压在（）以上，电流约为（）。磁控管平均寿命为（）。
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