Refer to figures.
QDM = Magnetic Direction from the aircraft to the station. (DM --> Direction Magnetic)
QDR = Magnetic Bearing from the station to the aircraft. (DR --> Direction Reciprocal)

In this case, we are using a Relative Bearing Indicator (RBI), which simply uses a fixed card (pointed North-up) and an ADF pointer on top, giving a bearing towards the NDB relative to the direction the aircraft is pointing. It is easier in this configuration to imagine the ADF pointer on top of the nearby Direction Indicator (DI), to effectively make it into an RMI (Radio Magnetic Indicator), which is a more complex instrument that covers both functions. The RBI can also be used mathematically by adding the relative bearings to the current magnetic heading, to find the QDM of the aircraft. The QDM of the aircraft is represented by the head of the needle (when using an RMI, or by imagining the RBI on top of the DI in this question), and the QDR is the reciprocal, so the tail of the needle.

For example, currently the DI is at a heading of 120°, and the RBI is showing 90° to the left of the nose, (Relative Bearing 270°), so the QDM is 030° (see one of the annexes above for a visual representation). This makes the tail of the needle, and therefore QDR, currently 210°.

Now lets try each possible answer (all degrees are in magnetic):

• Maintaining a heading of 120° would not bring us any closer to having a QDM of 240° (Radial 060°).
• Maintaining a heading of 120° would also not bring us any closer to having a QDR of 240° (Radial 240°).
• Turning onto a heading of 210° would mean we stay on our radial, and therefore maintain our current QDM and QDR, and our QDM is currently 210°, not 030°
• Turning onto a heading of 030° would also mean that we stay on our radial, and therefore maintain our current QDM and QDR, our QDM is 030°, so this answer is correct!