单项选择题 You have an SQL query that takes one minute to execute. You use the following code segment to execute the SQL query asynchronously. Dim ar As IAsyncResult = cmd.BeginExecuteReader() You need to execute a method named DoWork() that takes one second to run while the SQL query is executing. DoWork() must run as many times as possible while the SQL query is executing. Which code segment should you use?（）

单项选择题 You have an SQL query that takes one minute to execute. You use the following code segment to execute the SQL query asynchronously. IAsyncResult ar = cmd.BeginExecuteReader(); You need to execute a method named DoWork() that takes one second to run while the SQL query is executing.DoWork() must run as many times as possible while the SQL query is executing. Which code segment should you use?（）

单项选择题 You create a Web Form. The Web Form uses the FormView control to enable a user to edit a record in the database. When the user clicks the Update button on the FormView control, the application must validate that the user has entered data in all of the fields.You need to ensure that the Web Form does not update if the user has not entered data in all of the fields. Which code segment should you use?（）