Final answer:
Option (D), To improve temporal resolution in color Doppler, decreasing the sample size is the effective adjustment as it allows a quicker refresh and real-time update on flow or tissue movement.
Step-by-step explanation:
To improve temporal resolution on color Doppler, the correct option is D) Decrease sample size. This adjustment can potentially reduce the time needed to acquire data, enhancing the temporal resolution. It allows the color Doppler to refresh more quickly and provide real-time information on blood flow or tissue movement. Interventions such as increasing the wall filter might reduce low-velocity signals, steering the sample box adjusts the viewing angle, and increasing color gain may improve color fill but can cause oversaturation if not adjusted carefully; none of these specifically target an improvement in temporal resolution.