“the oldest”与“the eldest”的区别

英语的完型填空
The oldest stone buildings in the world are the pyramids.They have stood for nearly 5,000 years,and it seems likely that they 41 continue to stand for thousands of years yet.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 42 of these are the “Step” pyramid and the “Bent” pyramid.
Some of the pyramids still look much as they must have done when they were built thousands of years 43 .Most of the damage suffered by the others has been at the hands of men who were looking for treasure or,more often,for stone to use in modern buildings.The dry climate of Egypt has helped to preserve the pyramids,and their very shape has made them 44 likely to fall into ruin.These are good reasons why they can still be seen today,but perhaps the most important is that they were planned to last forever.
It is practically certain that plans were made for the building of the pyramids because the plans of 45 large works have fortunately been preserved.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 46 ,archaeologists have formed a fairly clear picture of them.
One thing is certain:there must have been months of careful planning 47 they could begin to build.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 48 ,and certain problems had to be overcome.
The step pyramid had to be on the west side of the Nile,the side on which the sun sets.This was for 49 reasons.It also had to stand well above the level of the river to protect it against the regular floods.It could not be too far from the Nile,however,as the stones to build it needed to be carried in boats down the river to the nearest point.Water transport was,of course,much easier than land transport.The builders also had to 50 a rock base which was not likely to crack under the great weight of the pyramid.Finally,it had to be near the capital,or better still,near the king’s palace so that he could visit it easily and personally check the progress being made on the final resting place for his body.
41.A.shall B.will C.would D.must
42.A.notorious B.known C.notice D.famous
43.A.ago B.before C.early D.earlier
44.A.much B.little C.more D.less
45.A.another B.the other C.other D.an other
46.A.found B.finding C.founded D.founding
47.A.early B.earlier C.before D.ago
48.A.followed B.made C.done D.banned
49.A.divine B.Christian C.Catholic D.religious
50.A.found B.find C.set D.build
数字那就是空啊。
为什么保证全对？那么确定么？