When the pressure exerted on a parcel of air decreases (as happens, for example, when air rises), the parcel will expand.
(the pressure; exerted; on a parcel of air) (air; rises; ) (the parcel; will expand; T:When the pressure exerted on a parcel of air)
the pressure air the parcel
exerted rises will expand
on a parcel of air
T:When the pressure exerted on a parcel of air