一个最简真分数，分子和分母的和是15，这样的分数有几个？[ ]
A．1
B．2
C．3
D．4
E．5
F．8
答案：D
Up till now we _______ four units and this will be the second time that we _______ a test.
A．have finished; have had
B．finished; will have
C．have finished; are to have
D．will finish; have had
公司债券的发行招标日为T-2日。（ ）
