Corrections

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Text from HakanHitit - English

Title
- The PRESENT PERFECT TENSE and PRES. PERFECT CONTINUOUS TENSE ?
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Sentence 1
- 1-I have studied English for 3 weeks by now.
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Sentence 2
- 2-I have been studying English for 3 weeks by now.
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Sentence 3
- 3-I have studied English often when I was young.
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Sentence 4
- 4-I have studied English for many years at university before.
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- ADD a NEW CORRECTION! - Sentence 4