(1) Q=cm△t shows that when the same heat is absorbed in the same mass of water and kerosene, the indication of the thermometer does not change obviously because of the large specific heat of water and the small degree of temperature rise;

(2) Q=I2Rt indicates that the current flowing through the two resistors is equal to the energization time, and the thermometer reading in bottle B rises rapidly, indicating that the resistance wire in bottle B generates more heat, and the resistance of copper wire in bottle A is smaller than that of nickel-chromium alloy wire in bottle B, so it can be concluded that the greater the conductor resistance, the more heat will be generated when the current and energization time are the same;

(3) To ensure that the currents flowing through the two resistors are always equal, the resistors are connected in series; At the same time, it is ensured that their power-on time is equal, and the heat generated in the conductor is only related to the resistance, so the control variable method is adopted.

The heat absorption of kerosene is reflected by the change of thermometer, and the conversion method is adopted.

Therefore, the answer is: (1) less than; (2) When the current and the power-on time are the same, the greater the conductor resistance, the more heat will be generated; (3) Control variable method or conversion method.