Criteria matched value to show up in drop down automatically

Criteria matched value to show up in drop down automatically

Hi guys, Kindly help me for following two things.

When I use lookup filed, the value that matched with criteria (only one value) cannot show up in drop down (Look Up Field) automatically and I need to choose again for this value. How can I overcome this ???? Please refer me for sample script. 

can I pass parent form's field input value (From Look Up field drop down) into sub form and also vice visa. ??? 

BR,
zzw