刀具的种类很多，但不论其结构如何变化，其切削部分总是以（）体为基本切刃。
参考答案：楔形
All the books donated by the students from urban schools are said _____ to the students in rural areas
the other day. [ ]
A. to be sent
B. being sent
C. having been sent
D. to have been sent
在金铸币本位制下，假定英国与美国的铸币平价为4.9100美元，两国之间运送1英镑黄金的费用为0.02美元，则美国的黄金输出点是（）。
A、4.9300
B、4.8900
C、4.9100
D、4.9000
