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