Exercise 17. Use the verb in brackets in either Perfect Simple or Perfect Continuous form.
1. He (not to work) very well recently. 2. He (not to work) for years. 3. I (to learn) irregular verbs all afternoon. 4. I (to learn) irregular verbs – ask me any. 5. I am tired – I (to calculate) our expenses all day. 6. I (to calculate) our expenses – we spend too much on clothes. 7. Sorry about the mess - the workers (to install) new computers in my office. 8. The workers (to install) new computers and we can start working now. 9. They (to monitor) the situation since the elections started. 10. They (to monitor) the situation – here is their report.

* Compare the use of Present Perfect and Past Indefinite:
e.g. We have just seen them (a past action which time is not definite) –Present Perfect.
We saw them last week (a past action, completed at a definite time in the past) –Past Indefinite.

1. He hasn't been working very well recently. 2. He hasn't worked for years. 3. I have been learning irregular verbs all afternoon. 4. I have learnt irregular verbs – ask me any. 5. I am tired – I have been calculating our expenses all day. 6. I have calculated our expenses – we spend too much on clothes. 7. Sorry about the mess - the workers have been installing new computers in my office. 8. The workers have installed new computers and we can start working now. 9. They have been monitoring the situation since the elections started. 10. They have monitored the situation – here is their report.