User decision work item

Hi All...., i want to ask...

I created user decision, and i enter list of agent for that user decision ( usr1 and usr2 ),

when work item in usr1 is executed, work item in user2 is automatically disappear.

how can i make the work item in usr2 don't disappear and

how can the work item will sent to usr2 only if work item in usr1 is approve..

thanks before