The northeastern part of China...,

[Silverobama]

I talked to a foreign student last night and he asked me a question "Are some parts of your country colder than others?"

My reply was "The northeastern part of China, cities like Harbin could be the coldest part of the country and the temperature could drop to minus 40 degree celsius every year. I think this has mainly to do with its geographical location, it's quite close to Russia. Another reason is its latitude, this makes the area receives less sunlight and therefore it becomes cold."

Please help me with a natural version of my reply.

 

[tedmc]

The (province of Heilongjiang in the) northeastern part of China with cities like Harbin could be (is) the coldest part of the country. and the Temperatures could (can) drop to minus 40 degree Celsius every year. I think this has mainly to do with its geographical location, it's which is quite close to Russia. Another reason is its latitude, this which makes the area receives less sunlight and therefore it becomes is cold.

Your second and third sentences are run-on sentences.

The use of "could" implies that your are not sure of the facts, which I thought are quite straightforward.

The northeastern part of Chinese is not Harbin as you have written; Harbin is just a city within the part.

The northernmost part of China where Harbin is is of course the coldest, as it is furthest away from the equator (high latitude). The intensity and duration (as in daylight hours) of sunlight decrease with latitude.