You work in a company which uses SQL Server 2008. You are the administrator of the company database. Now you are in charge of a SQL Server 2008 instance. A user reports that when he runs a query, it takes a quite long time and it is still unfinished. As the IT support, you have to verify whether the query is blocked.  Which tool should you use? （） 

• A、You should use the Database Engine Tuning Advisor tool 
• B、You should use the Windows System Monitor tool 
• C、You should use the Job Activity Monitor tool in Microsoft SQL Server Management Studio 
• D、You should use the Activity Monitor tool in Microsoft SQL Server Management Studio