B, from the above analysis: E=BLat, and e = △φ△t, then: △φ△t = blat ∝ t, so B is correct.
C the average value of the induced electromotive force in the loop is: E = △φ△ t, and the induced current is:. I = ER+r,
The amount of charge passing through the metal bar q =. i△ t = △φ? R+r=BLxR+r=BL? 12at2R+r, which means q ∝ t2; Then the φ-T image should be a parabola, so C is wrong.
The potential difference between d, a and b is U=RR+rE=RR+rBLat∝t, so d is correct.
So: BD.