This exercise contrasts two tenses: Present Perfect Simple and Continuous. Sentences are given in pairs to emphasize the contrast. The answer key includes a short justification, which might be helpful to independent learners.
I have been teaching since 1999. I worked as a secondary school English teacher for 16 years, but now have my own business tutoring/teaching children and adult learners. Being self-employed, I can finally breathe and use my work time effectively. I also write a blog - creating ESL exercises based on authentic texts.