A sheet is placed on a horizontal surface in front of a strong magnetic pole. A force is needed to:

A. hold the sheet there if it is magnetic.

B. hold the sheet there if it is non-magnetic.

C. move the sheet away from the pole with uniform velocity if it is conducting.

D. move the sheet away from the pole with uniform velocity if it is both, non-conducting and non-polar.

Choose the correct statement(s) from the options given below:

Let us analyze each statement to determine when a force is required to hold or move a sheet in front of a strong magnetic pole:

Statement A: "hold the sheet there if it is magnetic."
If the sheet is magnetic (specifically ferromagnetic, like iron), it will be attracted to the strong magnetic pole. To keep it stationary (hold it there) and prevent it from flying towards the pole, an external force must be applied in the opposite direction to balance this magnetic attraction. Therefore, a force is needed, and Statement A is correct.

Statement B: "hold the sheet there if it is non-magnetic."
If the sheet is non-magnetic, there is no static magnetic force acting on it when it is stationary in the magnetic field. Thus, no external force is needed to hold it in place. Therefore, Statement B is incorrect.

Statement C: "move the sheet away from the pole with uniform velocity if it is conducting."
If the sheet is conducting (even if it is non-magnetic, like copper or aluminum), moving it away from the magnetic pole changes the magnetic flux passing through the sheet. According to Faraday's law of electromagnetic induction, this change in flux induces electromotive force (emf) and consequently circulating eddy currents within the conducting sheet. According to Lenz's law, these induced currents will create a magnetic field that opposes the motion that created them. Thus, an opposing electromagnetic drag force will act on the sheet as it moves. To maintain a uniform velocity, an external force must be applied to overcome this opposing drag force. Therefore, a force is needed, and Statement C is correct.

Statement D: "move the sheet away from the pole with uniform velocity if it is both, non-conducting and non-polar."
If the sheet is both non-conducting and non-polar, no eddy currents can be induced (since it is non-conducting), and no electric polarization forces will act on it. Hence, there is no electromagnetic interaction or drag when moving it through the magnetic field. Therefore, no force is required to move it with uniform velocity, making Statement D incorrect.

Conclusion:
Only statements A and C are correct. Thus, the correct choice is "A and C only".