Lenz's law: The long straight wire in the figure carries a current I that is decreasing with time at a constant rate. The circular loops A, B, and C all lie in a plane containing the wire. The induced emf in each of the loops A, B, and C is such that

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According to Lenz's law, the induced emf in a loop opposes the change in magnetic flux through the loop. As the current in the wire decreases with time, the magnetic field around it also decreases. This change in magnetic flux induces an emf in the loops. 
For loop A, the induced magnetic field opposes the decreasing magnetic field of the wire, so the emf is in a direction that creates a magnetic field that enhances the original field. This means that the induced emf creates a counter-clockwise current that opposes the decrease of the original current. Therefore, the induced emf has a clockwise direction.
For loop B, the plane of the loop is perpendicular to the magnetic field of the wire, so there is no change in magnetic flux through the loop, and hence no induced emf.
For loop C, the induced magnetic field opposes the decreasing magnetic field of the wire, so the emf is in a direction that creates a magnetic field that opposes the original field. This means that the induced emf creates a clockwise current that opposes the decrease of the original current. Therefore, the induced emf has a counter-clockwise direction.

Lenz's Law: the Long Straight Wire in the Figure Carries