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The atomic bomb

“The Manhattan project” was the name of a secret organization concealead by the USA .It’s purpose was to creat the atomic bomb.It was active from 1939 until 1945.The man who oversaw the entire project,from conception until completion,was called Robert Openhheimer. In 1945 USA have used this bombs twice on the Japanese cities of Nagasaki and Hiroshima The first bomb hit Nagasaki and it was named “little boy”.The second bomb was called “fatman” and landed in Hiroshima 3 days later

Evidence from this occasions,as well as atmospheric nuclear testing and nuclear power accidents have formed the basis of ower knowledge concerning the effects of a nuclear bomb One of this side effect might be the nuclear winter Dense smoke from a nuclear war,will block the sun.Because of the smoke there will be no warmth and sunlight,pludging the world into darkness.

Can someone help me with a review concerning the grammatical errors that i might have made?