普碳钢配件焊修前，应清除施焊表面离焊缝边缘不小于（）mm范围内的油垢及氧化物。
A.10
B.20
C.30
参考答案：B
协议承诺原则的核心主要体现在要求借款人通过签订贷款合同等协议文件承诺（）。
A、申贷材料信息的真实有效
B、贷款的真实用途
C、贷款资金的支付方式
D、各方的权利义务
The one-year spot rate is 6 percent and the one-year forward rates starting in one, two and three years respectively are 6.5 percent, 6.8 percent and 7 percent. What is the four-year spot rate（）
A. 6.51%.
B. 6.58%.
C. 6.57%.
