Crystal Reports sub-reports without having to be prompted for para

Message

   I am still very new to crystal and am tryng to use a sub-report 

I am using crystal reports and have a report with a sub-report.  The main report has 3 parameters and the sub-report has 2 parameters.  These 2 are used inside the sql select statement. Their names are Sel_Po_Nbr and Sel_Track_Id.

On the main report, there is a Po_nbr field that matches the Sel_po_nbr and a track_id field that matches the Sel_track_id, but when I try to link them, I cannot seem to get it to work.

The main report that has three parameters, how can I link the sub-report so I am only asked the three parameters and not all five?  

thanks 
Tony c.