Explanation: Figure 3D7 illustrates an operational amplifier (op-amp) configured as a summing inverter. In this common op-amp configuration, the output voltage is proportional to the sum of the input voltages. Critically, because the input signals are applied to the inverting input of the op-amp, the output signal will be inverted relative to the sum of the inputs. Assuming the circuit is designed for unity gain (where the input resistors and feedback resistor are equal), the output voltage will simply be the negative sum of the input voltages. If the combined DC input voltages sum to a positive +5.5 V, the summing inverter circuit will produce an output voltage of -5.5 V. Therefore, option D is correct because it reflects both the summation of the input voltages and the inversion inherent to this op-amp configuration. Option B (+5.5 V) is incorrect as it fails to account for the signal inversion. Options A and C are incorrect as they represent significantly different voltage values.