Click the Exhibit button. Given this code from Class B： 25. A a1 = new A（）； 26. A a2 = new A（）； 27. A a3 = new A（）； 28. System.out.println（A.getInstanceCount（））； What is the result？（） Compilation of class A fails.。 Line 28 prints the value 3 to System.out.。 Line 28 prints the value 1 to System.out.。 Compilation fails because of an error on line 28.。 A runtime error occurs when line 25 executes.。
以下不属于导致水泥砂浆防水层起砂缺陷的原因是（）。 砂浆搅拌时加水过量。 使用的水泥强度等级过低。 养护不当。 基层清理不当。
海轮1301，1211，最适合灭（）火灾 D类即电气火。 金属火灾。 固体火。
Examine the data in the EMPLOYEES table. EMPLOYEES EMP_NAME DEPT_ID MGR_ID JOB_ID SALARY EMPLOYEE_ID 101 Smith 20 120 SA_REP 4000 102 Martin 10 105 CLERK 2500 103 Chris 20 120 IT_ADMIN 4200 104 John 30 108 HR_CLERK 2500 105 Diana 30 108 IT_ADMIN 5000 106 Smith 40 110 AD.ASST 3000 108 Jennifer 30 110 HR_DIR 6500 110 Bob 40 EK_DIR 8000 120 Revi 20 110 SA_DIR 6500 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: DELETE employee_id, salary, job_id FROM employees WHERE dept_id = 90; 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.。
竞争性拮抗药效价强度参数PA2的定义是（） 使激动药效应减弱一半时的拮抗剂浓度的负对数。 使加倍浓度的激动药仍保持原有效价强度的拮抗剂浓度的负对数。 使拮抗药始终保持原有效价强度的激动药浓度的负对数。 D，使激动药效应减弱至零时的拮抗剂浓度的负对数。 使激动药效应加强1倍的拮抗剂浓度的负对数。
Which two changes and their effect on the system can be tested by using the Database Replay feature？（）
