Choose the word or phrase that best fits the blank space.
The building of the pyramid in Ancient Egypt obviously required a vast labour force, but the (36) ______ image of gangs of Egyptians being forced to work is probably incorrect. In fact it seems that though prisoners of war did some of the heavy work and the maintenance jobs, most of the (37) ______ labourers were farmers who worked during the flood periods when farming was impossible anyway. The labourers were probably paid in food - because money did not yet (38) _____ and organised in groups with encouraging names such as 'Hardworking Gang' or 'Strong Gang'. Although the traditional picture of thousands of slaves being struck with whips is unlikely to be "true, paintings do show supervisors carrying metre-long sticks which were not simply (39) ______ of office. One architect, Nekhebu, boasted that he never hit a workman hard enough to knock him down. The Greek historian Herodotus gave traditional figures for the work force of one of the pyramids as 100;000 men replaced (40) ______ three months for a period of 20 years. It is impossible to prove or disprove these figures, but they had doubtless been wildly overestimated. Housing that was found in the desert to the west of one of the pyramids would have accommodated a permanent work force of no more than 4000.
(40) ______
A.each
B.by
C.after
D.every