耶克斯－多德森定律描述了学习动机与学习效果之间的关系根据该定律，以下描述正确的是（） ["任务难度中等时，最佳动机激活水平也中等","动机水平越高，学习效果越好","任务较难时，最佳动机激起水平较低","任务较容易时，最佳动机激活水平较高"]
You want to track and store all transactional changes to a table over its lifetime. To accomplish this task， you enabled Flashback Data Archive with the retention of 5 years. After some time， the business requirement changed and you were asked to change the retention from 5 years to 3 years. To accomplish this， you issued the following command： ALTER FLASHBACK ARCHIVE fla1 MODIFY RETENTION 3 YEAR； What is the implication of this command？（） [" The command produces an error because the retention time cannot be reduced."," All historical data is retained but the subsequent flashback data archives are maintained for only three years."," All historical data is purged and the new flashback data archives are maintained for three years."," All historical data older than three years is purged from the flashback archive FLA1."]
失业人员在领取失业保险金期间，停止参加职工基本医疗保险，不享受基本医疗保险待遇。
花灌木类
下述哪种剂量可产生副作用（） ["治疗量","极量","中毒量","阈剂量","无效量"]
静平衡法的实质是确定旋转件上不平衡量的（）和（）。
