1) By the time Graham arrived at the train station, the train had already left.
2) How long had you been trying to call Tom before he finally answered the phone.
3) The children had put away their toys before their mum came back home.
4) Alan had a headache because he had been playing computer games all afternoon.
5) Simon had been saving money for many years before he bought his own house.
6) The football game had just started when it began to rain.
1. to correct
2. correct
3. correcting (more likely) / correct
4. to correct
5. correct
6. saw; was correcting
7. is correcting; has been correcting
8. be corrected
9. corrects / has corrected; will learn
10. had already corrected
11. corrects
12. has not corrected
13. were corrected
14. corrected
15. will correct
16. I can't see the end of the sentence, but I believe the answer is: "will be corrected"
9. Our son always phones us every day.
10. Is your sister at home? - I need to speak to her.
don't always
Fred often
is never
Layla usually
I sometimes
is always
they seldom