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。
《工程建设强制性条文》（水利工程部分）规定，沥青混凝土防渗墙施工时（）。 应进行现场铺筑试验，以确定沥青混合料的施工配合比、施工工艺参数，并检查施工机械的运行情况等。 接触沥青的人员，应发给必要的劳保用品和享受保健待遇。 模板拆除时间应根据混凝土已达到的强度及混凝土的内外温差而定，应在夜间或气温骤降期间拆模。 沥青混凝土制备场所，要有除尘、防污、防火、防爆措施，并配各必要的消防器材。 斜坡施工应设置安全绳或其他防滑措施。机械由坝顶下放至斜坡时，应有安全措施，并建立安全制度。
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.。
A型行为模式
In which scenario， will you issue the following command？（）
RMAN> REPORT NEED BACKUP DAYS 7；
