根据《招标投标法》的规定,招标人和中标人应当自中标通知书发出之日起( )日内,按照招标文件和中标人的投标文件订立书面合同。
A.5
B.15
C.20
D.30
参考答案:D
The head of the company promised to deal with matters of this sort _____he returned to his office.
A.until
B.while
C.by the time
D.the moment
铁路线路的等级是如何划分的?