8) She has never got good marks at Math but she doesn't worry about it. In American English, it should be "She has never gotten good marks in math, but she doesn't worry about it." I believe British English uses "got" as the past participle of "get" though. See http://learnersdictionary.com/definition/get In American English, you also say "in math", "in science", "in social studies", etc. instead of "at math", etc. I think "at math" is purely British English. 9) Alice always shows off! Isn't it foolish from her part? It should be "Alice always shows off! Isn't it foolish on her part?" in American English. 10) I think we have had a wonderful trip about Australia. In American English, it should be "I think we have had a wonderful trip to Australia." or perhaps even more naturally as "I think we had a wonderful trip to Australia". 11) Such behaving in your age is really foolish. In American English, it should be "Such behavior at your age is really foolish." You could also say "Behaving like that at your age is really foolish." if you want to actually use the word "behaving". 12) You took Father's car without his permission. It's dumb and foolish. If the person saying this is your sister or brother, then it should be "You took dad's/father's car without his permission. It was dumb and foolish." I think Americans say "dad" more often in this situation. If the person is not your brother or sister, then it should be "You took your father's car without his permission. It was dumb and foolish."

1) In those days I was only a foolish and naive lad. This is grammatically correct but I think it would sound more natural as "In those days, I was a foolish and naive kid." or as "In those days, I was a really foolish and naive kid." 2) Don't you mind if I close the door? There is a lot of noise in the hall. It should be "Do you mind if I close the door? There is a lot of noise in the hall." 3) The children crept upstairs trying not to wake up their parents. (correct) 4) It won't do you any harm if you spend more time outdoors. Grammatically correct but Americans will probably say "It is okay if you spend more time outdoors." instead if a child is asking if they can play outside longer. If you are telling someone that they should go outside more for their health though, then "It wouldn't hurt you to spend more time outdoors." would sound more natural in American English. 5) The teacher looked at Nick and he hid his cheat-sheet in the desk. It should be "The teacher looked at Nick so he hid his cheatsheet in the/his desk." I would usually write "in his desk" here instead of "in the desk". It just sounds a little more natural in American English. If you use "and" instead of "so", it sounds like the two actions aren't related. By the way, I think most Americans would say this as: "When the teacher looked at Nick, he hid his cheatsheet in his desk." "The teacher looked at Nick so he hid his cheatsheet in the/his desk." is grammatically correct though. :) 6) Whenever he goes shopping he always buys rotten fruits and vegetables. It should be "Whenever he goes shopping, he always buys rotten fruit and vegetables." Note that fruit is a mass noun so you don't say "fruits" here. Also, you need a comma after "shopping". 7) When we were at the camp we cooked a dish with a very unusual taste. This is grammatically correct but you should put a comma after "camp". When we were at the camp, we cooked a dish with a very unusual taste.

No idea about the translation but better English is: 1) In those days I was only a foolish and naive lad. OK 2) Do you mind if I close the door? There is a lot of noise in the hall. 3) The children crept upstairs, trying not to wake up their parents. 4) It won't do you any harm if you spend more time outdoors. OK 5) The teacher looked at Nick SO he hid his cheat-sheet in the desk. 6) Whenever he goes shopping he always buys rotten fruit and vegetables. 7) When we were at the camp we cooked a dish with a very unusual taste.OK 8) She has never got good marks at maths but she doesn't worry about it. 9) Alice always shows off! Isn't it foolish ON her part? 10) I think we have had a wonderful trip to/around Australia. 11) Such behaviOUR AT your age is really foolish. 12) You took father's car without his permission. It WAS dumb and foolish.