题目内容：
When the builder starts to build a house, his estimate will have to be corrected and re-vised because___________ .
A．it is wrongly worked out by a workman B．the future owner of the house thinks the estimate is so high that he cannot afford the building
C．the prices of building materials and the expenses of labor may be different from the original prices and expenses
D．estimates are usually mistaken in the beginning
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