I
adverb
BAD : I'll go with you as long as I won't have to sing.
GOOD : I'll go with you as long as I don't have to sing.
II
adjective
BAD : I am afraid it will take long to improve my English.
GOOD : I am afraid it will take a long time to improve my English.
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Use take long in questions and negative sentences: 'How long does it take to get to London by train?' 'It doesn't take very long.'
Use take a long time in affirmative sentences: 'It might take a long time to sort out the problem.'