下面电泵系统的三种流程中，完全正确的是（） ["电泵供电流程：油气分离器→多级离心泵→单流阀→池油阀→油管→井口→输油系统","电泵抽油系统：地面电网→变压器→控制箱→接线盒→电缆→电机","电力讯号传输系统：井下压力检测装置→电机绕组→电缆→地面电"]
Which statement is true？（） ["Compilation fails because the hashCode method is not overridden.","A HashSet could contain multiple Person objects with the same name.","All Person objects will have the same hash code because the hashCode method is not overridden.","If a HashSet contains more than one Person object with name="Fred"， then removing another Person， also with name="Fred"， will remove them all."]
焊接安全的措施有：防止触电、（）、防止辐射、防止粉尘及有害气体等。
氮源
Examine the data in the EMPLOYEES table. On the EMPLOYEES table, EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID. The JOB_ID column is a NOT NULL column. Evaluate this DELETE statement: Why does the DELETE statement fail when you execute it?（） [" There is no row with dept_id 90 in the EMPLOYEES table."," You cannot delete the JOB_ID column because it is a NOT NULL column."," You cannot specify column names in the DELETE clause of the DELETE statement."," You cannot delete the EMPLOYEE_ID column because it is the primary key of the table."]
简述学前儿童游戏教育实施的组织内容。
