补全短文the oldest stone buildings
the oldest stone buildings in the world are the pyramids. they have stood for nearly 5，000 years， and it seems like that _____(1)_____。 there are over eighty of them scattered along the banks of the nile， some of which are different in shape from the true pyramids. the most famous of these are the "step" pyramid and the "bent" pyramid.
some of the pyramids still look much the same as they must have done when they were built thousands of years ago. most of the damage suffered by the others has been at the hands of men who were looking for treasure or， more often， ____(2)____。 the dry climate of egypt has helped to preserve the pyramids， and their very shape _____(3)_____。 these are good reasons why they can still be seen today， but perhaps the most important is that they were planned to last for ever.
it is practically certain that plans were made for the building of the pyramids_____(4)____。 however， there are no writings or pictures to show us how the egyptians planned or built the pyramids themselves. consequently， we are only able to guess at the methods used. nevertheless， by examining the actual pyramids and various tools which have been found， archaeologists have formed a fairly clear picture of them.
one thing is certain： there must have been months of careful planning_____(5)_____。 the first thing they had to do was to choose a suitable place. you may think this would have been easy with miles and miles of empty desert around， but a pyramid could not be built just anywhere. certain rules had to be followed， and certain problems had to b overcome.
exercise：
a for stone to use in modern buildings
b has made them less likely to fall into ruin
c before they could begin to build
d because the plans of other large works have fortunately been preserved
e while building the pyramids
f they will continue to stand for thousands of years yet
key：fabdc