A, the magnetic induction intensity increases. According to Lenz's law, the direction of induced current is acbda, so A is correct;

B, according to Faraday's law of electromagnetic induction, the induced electromotive force e = △ φ△ t = s△ b△ t = l× L2×△ b△ t = △ b△ t? L22, so b is correct;

C, acb section conductor is equivalent to the power supply, the current flows from A to B, and the current flows from the low potential point inside the power supply to the high potential point, so the potential at point A is lower than that at point B, so C is wrong;

D, let the total resistance of the conductor be R, then the potential difference between point A and point B Uab=ER×R2=△B△tl24, so D is wrong;

So choose ab.