在贸易通系统中作未用退回处理(撤票)的电子商业汇票的票据状态应该为()。
A、出票已签收
B、提示承兑待签收
C、提示承兑已签收
D、转让背书待签收
参考答案:A, C
已知数列{an}满足an=n•2n,则其前n项和是( )
A.(n-1)2n+1-2
B.(n-1)2n+1+2
C.(n-1)2n-2
D.(n-1)2n+2
We ______ for one hour and a half and it is about time we ______ a rest.
A.trained; take
B.have trained; took
C.are training; will take
D.had trained; to take