题目内容：
When the builder starts to build a house, his estimate will have to be corrected andrevised 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 originalprices and expenses
D．estimates are usually mistaken in the beginning
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答案解析：