D

Step 1: When a soft iron piece is placed in a galvanometer, it enhances the magnetic field due to its high magnetic permeability.
Step 2: This enhancement can lead to the production of a radial uniform magnetic field inside the coil, which is desirable for the proper functioning of a galvanometer as it ensures that the magnetic field lines are uniformly distributed.
Step 3: With a strong magnetic field, the current passing through the coil causes a steady deflection since the torque acting on the coil increases proportionally with the magnetic field strength.
Step 4: Therefore, the effects mentioned in all options (A, B, and C) occur simultaneously, indicating that all conditions are met when the soft iron piece is kept in the galvanometer.
Conclusion: Since all of the statements are true, the correct answer is D.