The great change in the twentieth century is about electricity-based technologies. They are a heating system, a cooling one and kitchen tools. With these technologies, people are likely to have a more comfortable and convenient life than in the past.
The great change< the prompt asks about the great change, so maybe another word, something creative? Of all the changes of the twentieth century,... or During the twentieth century, several new innovations changed the world, but electrical ones made the greatest impact. The list of 3 examples is a start. heating and cooling system, and computerized kitchenware. That last sentence is good. however, the prompt asks about the 20th century= 1900s, so maybe the effects/changes already occurred...and are still occurring? This intro works, but there's not much creativity in the language, the words you choose, the phrasing, "the great change...is about...technologies.. They..." is a tad non-parallel.
what is one change
you chose two changes? A/C (air conditioning) and kitchenware. Your explanations are ok.. but what do they REALLY tell about that are worth mentioning as the ONE and only change of the twentieth century? Yes, A/C is great, it saves people from the harsh cold/heat, but what else does it do? it controls the environment, allows people to live even in the Arctic/Antarctic, or even in the middle of deserts, A/C allows people to regulate food temperature/freeze food, stabilize things for reaction/research/ ship food across countries w.o just ice packing..Be creative! yes electrical appliances were a great change, but what else other than parties :]
About writing skill, the conclusion is better I think than what I read last time. you try to lead into other topics...however, place your topic more in the scope of the change.
They are able keep people healthy without any ailments during the winter and summer period and
Good. but A/C keeps people comfortable, not healthy? well, somewhat healthy, but that's more about diet. however, since you talked about frying pans, steam cookers, etc, this sentence doesn't address that part of the change. If you want, you can mention how these electrical changes are not just those valuable to heating/cooling homes, but also allow people to cook in these more controlled environments. again, creativity to connect what you write about.