Both the North Pole and the South Pole are colder than the tropics. Consequently, the thickness in the 1000-300 mb layer is smaller at high latitudes than at low latitudes in BOTH hemispheres. This means that a northward directed PGF increases with height in the NH while a southward directed PGF increases with height in the SH. Since the COR force acts to the right of the motion (at right angles) in the NH and to the left of the motion (at right angles) in the SH, the jet stream winds flow from generally from west to east in BOTH hemispheres. Thus, the correct answer here is (a).