The ancient monument of Stonehenge is one of the most spectacular sights of southern England. Why Stonehenge (A11) ... is still a mistery. There was a theory which stated that it (A12) ... a type of astronomical clock or calendar, by which the people of that time (A13) ... the seasons, hours of the day and the phases of the moon. However, up till now this theory (A14) ... . But there is no doubt that if the people who (A15) ... Stonehenge (A16) ... considerable engineering skills they (A17) ... to raise the enormous stones to make up the monument. Stonehenge is structurally unique among European prehistoric monuments and (A18) ... a large number of visitors every year. Quite recently the government (A19) ... the closure of the site because a number of stones (A20) ... to be unstable and now the remarkable monument can only be seen from a distance.
A11. 1) has built 2) had built 3) was building 4) was built
A12. 1) has been 2) had been 3) was 4) was being
A13. 1) had calculated 2) were being calculated 3) had been calculated 4) were calculated
A14. 1) hadn't proved 2) hadn't been proved 3) didn't prove 4) hasn't been proved
A15. 1) were building 2) had been built 3) were built 4) have been building
A16. 1) didn't possess 2) were not possessing 3) hadn't possessed 4) were not possessed
A17. 1) weren't able 2) wouldn't be able 3) hadn't been able 4) wouldn't have been able
A18. 1) is attracted 2) attracts 3) was attracting 4) has been attracted
А19. 1) has announced 2) had announced 3) was announced 4) was announcing
A20. 1) are considering 2) are considered 3) have considered 4) had been considering