Change the current of the power supply to -5 A, and repeat the previous two experiments. Select all of the following statements that are true when the current of the power supply is -5 A.
A. The induced emf (or voltage) in the loop is never positive when the loop is moving to the right.
B. When the loop enters the region between the Helmholtz coils, the induced emf (or voltage) is positive.
C. When the loop exits the region between the Helmholtz coils, the induced emf (or voltage) is negative.
D. The induced emf (or voltage) in the loop is never negative when the loop is moving to the left.