1. The correct sentence is "The last time I wrote a letter was 5 years ago." 2. The correct sentence is "How long have you built the house?" 3. Both sentences are correct. 4. The correct sentence is "She has worked as an accountant for 2 months." 5. The correct sentence is "He has played football since he was 6 years old." 6. Both sentences are correct. 7. The correct sentence is "This is the first time I have seen such a beautiful girl." 8. The correct sentence is "I haven't been to Japan for 4 years." 9. The correct sentence is "I have never eaten such a delicious cake before." 10. The correct sentence is "I have been learning English for 10 years." 11. The correct sentence is "How long have you had this car? When did you buy it?" 12. The correct sentence is "They have been studying Spanish since they were in grade 4." 13. The correct sentence is "Mary hasn't seen her aunt since she was 8 years old." 14. The correct sentence is "It's been over 4 years since they left their homeland."