建筑产品的特点之一是体积庞大，据统计同一货币量的建筑产品要比机械产品重()倍。
A.10～20
B.20～40
C.30～50
D.40～50
参考答案：C
Which of the following statements regarding long-term forecasts of cash flows is most accurate Long-term cash flow forecasts are:（）
A. constructed from recent daily and weekly cash flows.
B. are usually more accurate than short term cash flow forecasts.
C. based on pro-forma balance sheet projections for future years.
阴极保护系统中的阳极地床（）的来源。
A.不可能成为直流杂撒电流
B.可能成为交流杂散电流
C.可能成为直流杂散电流
D.不会成为杂散电流
