证券组合的可行域总是()。
A.左边界凸出
B.右边界凸出
C.左边界凹进
D.右边界凹进
参考答案:A
Jimmy said that he would come to pick me up, but he _______ by now.
A.hasn’t turned up
B.doesn’t turn up
C.won’t turn up
D.hadn’t turned up
感应同步器一般由1000Hz到()Hz。
A.10000
B.100000
C.1000000
D.10000000