(2) Device A can explore the relationship between current work and resistance.
(3) Comparing two different experimental devices, A and B, the better device is B, because the thermometer can accurately measure the temperature change of kerosene, which is convenient for quantitative research.
So the answer is: (1) expansion, (2) resistance, (3) b; Thermometer can accurately measure the temperature change of kerosene, which is convenient for quantitative research.