preposition
1
BAD : After the accident, I had to stay in hospital during three months.
GOOD : After the accident, I had to stay in hospital for three months.
BAD : It is difficult to concentrate during such a long time.
GOOD : It is difficult to concentrate for such a long time.
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During answers the question 'When?': 'During her stay here, she made a lot of good friends.'
For answers the question 'How long?': 'I've been learning English for two years.' 'We've been waiting here for almost an hour.'
2
BAD : My uncle has known me during all my life.
GOOD : My uncle has known me all my life.
BAD : The baby cried during all night long.
GOOD : The baby cried all night long.
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When a phrase saying 'how long' begins with all , there is no preposition: 'It rained all night.' 'He's been in bed all day.'
3
BAD : During waiting for the train, I met an old friend of mine.
GOOD : While waiting for the train, I met an old friend of mine.
BAD : This was my biggest problem during I was living in the United States.
GOOD : This was my biggest problem while I was living in the United States.
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See note at WHILE 1 (↑ while )