军官受到奖励的条件？
参考答案：
在作战和军队建设做出突出贡献或者取得显著成绩，以及为国家和人民做出其他较大贡献的，按照央军事委员会的规定给予奖励。
某发射机的载波频率为457.7MHz，载频误差为±5×10-6，则具体允许载频误差为（）Hz。
A、±562.7
B、±507.7
C、±2288.5
D、±456.2
—Have you heard from Nelly recently?
— Yes, I _________ his letters and cards many times while I was in Italy.
A．have received
B．received
C．had received
D．would receive
