期货从业人员可以在客户不知情的情况下，向客户的代理人和介绍人返还佣金。（）
参考答案：错
So difficult ______ it to work out the problem that I decided to ask Tom for advice.
A．I did find
B．did I find
C．I have found
D．have I found
常规静脉肾盂造影的首次摄片时间一般是注射对比剂后
A．1min左右
B．7min左右
C．30min左右
D．60min左右
E．90min左右
