Which of the following groups of farm equipment use electricity as their source of power?

The group of farm equipment that uses electricity as their source of power includes milking machine, incubator, and refrigerator. Milking machines are used to extract milk from animals using vacuum pressure, and they require a power source to run the vacuum pump. Incubators are used for hatching eggs and require electricity to maintain the appropriate temperature and humidity levels. Refrigerators are used for preserving agricultural produce and require electricity to run the compressor that maintains low temperatures inside the refrigerator. Therefore, options A is the correct answer.