approaching a class d airport with 3 runways,tower instructed "report midfield" . (no other instructions) what does this mean? 1-- to report abeam midfield on left downwind? 2-- or right downwind? 3-- which runway? or 4-- fly to the middle of the field and report midfield as i am over the middle of the field? i know best to ask for clarification. but controler is very busy. what did he mean?