． Put water, sugar water, and salt water into the refrigerator to cool down, and observe whether "ice" begins to form after a while - solidification. If it is found to be solidifying, use a thermometer to measure the temperature of the solid-liquid mixture - —that is, the freezing point. Finally

make a comparison and get the result.

Analysis: To explore whether the freezing points of sugar water, salt water and pure water are the same, we need to measure the freezing points of these three substances. However, the measurement of the freezing point is relatively inconvenient, so based on the fact that the freezing point and melting point of the same substance are the same, the melting points of these three substances can be measured instead, and the experimental process can be designed by referring to the melting experiment in the textbook.

Answer: (1) Take three small plastic cups and fill them with pure water, salt water and sugar water of the same quality respectively, and then put them in the refrigerator to freeze.

(2) After they have all frozen, take them out, crush them separately, and then put them into three small beakers.

(3) Use a thermometer to measure the temperatures at each moment during their melting process.

(4) The respective melting points of pure water, salt water and sugar water can be obtained from the experimental data, and the conclusion can be drawn