Leute sagen, dass ich nicht fleißig bin. Sie sagen, dass ich zu viel Musik höre und im Chemieunterricht nicht aufpasse. Aber das ist gar nicht so einfach. Bei Cello und Karate arbeite ich sehr hart. Deswegen habe ich wenig Zeit für die Schule.

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Die Sätze sind schon verständlich, aber nicht ganze Sätze. Die Sätze, wie sie jetzt stehen, sind kurze aber richtige Sätze.

Your sentences or understandable, but they are not complete sentences. The sentences in the second paragraph are short but complete sentences with subject, verb and objects.

"Akademiker" sind vielmehr die Personen.

"Academics" is more school or learning (das Lernen)

This is part two:

After visiting the tourist attractions, I went back to the places connected with my personal history. I have found my kindergarten and school, the school where my parents worked, and finally the house where we lived. We moved to Chkalovsk in 1993 and enjoyed living there. My parents remember our first year there as one of the happiest in their life. The serious economical crisis that was developing in the mid-1990s turned the city to poverty and depression. In 1998, my father got an invitation to work in Peru and we left Chkalovsk forever. I like Chkalovsk mostly for its scenery, for its wild but picturesque river quays and beaches, for its quiet streets with wooden houses and front gardens, from which one can hear the sizzling of grasshoppers or the crowing of roosters. I was happy to realise that nothing has changed there during the 20 years of my absence, and my parents, affected by nostalgia, got the desire to buy a summer house on one of the Chkalovsk quays.

private -- personal -- There is a difference in meaning. Private is more "secret" or "confidential". Personal relates more to myself. 

biography -- is more something written and usually after the end of milestone in the life of a person or organization or even after someone's death.

serious is a better word to go with crisis.

economical -- is actually a very different meaning. It is more like "efficient" or "inexpensive". For example: I drive an efficient, economical car.

    economic -- relates to the economy 

scenery -- is how nature looks -- mountain scenery, forest scenery, etc.

the sizzling of grasshoppers or the crowing of roosters -- you could also say: ...hear grasshoppers sizzling or roosters crowing...

That was a very interesting story and very well written. I enjoyed reading it. Thanks.

Hi Vera,

Your text was long enough that I decided to divide my comments into two sections. Here's part one:

Notes about my summer days.

"have never been" -- that would mean you still haven't been there, but earlier you said you "visited". So it's a small grammar point, but your writing is very good and I thought you would like to know that small difference.

You can use either "close to" or "near", but not "near to"

occupied -- can suggest that they are not paid, but rather just "kept busy". For example, "On holidays we occupied ourselves with reading and hiking and just sitting around."

examining -- would be more if the plane was on the ground and being looked at. I am sure he was in the air and flying it.

laconic -- that's not a very common word and probably not for architecture. In fact, I had to look up the meaning myself. I'd use something like "simple" as a contrast to pompous for architecture. 

Hi Akram,

May I suggest the following improvements to your text. I've included a few reasons after the suggestions.

emission of CO2 – the more common way to combine this thought it "CO2 emissions"

 I think: "As I see it" OR "In my opinion" OR "If you ask me" – these might be some nice alternatives to simply saying "I think..."

cars in order to preserve the atmosphere's purity– In English we don't usually talk about purity for the atmosphere. We do, however, often say "conserve OR preserve OR save the atmosphere"

This last is a – I think you can repeat "pollution" in the next sentence to make it clear and stronger.

despite of -- There are two expressions that mean the same thing and they often get mixed up: "in spite of" OR "despite" Here you could also say, "... in spite of the efforts...."

responsibles of many partnerships – In English we don't really simply use "responsibles" to refer to people in responsible positions. Therefore, I changed it a bit.You could add it again in the next sentence to call your readers to be responsible people when thinking about CO2 emissions.