Using variable in Web Services Task

Hi all,

I would like to ask how I can use the variable as the input parameter of web services task.

In microsoft 's document, http://msdn2.microsoft.com/en-us/library/ms187617.aspx, It suggests the for the value, If the Variable check-boxes are selected, select the variables in the list to provide the inputs; otherwise, type the values to use in the inputs. but I cannot find such Variable check-boxes.

It just want to know how I can check the Variable check-boxes.

Many Thanks

Spencer