I found _____ very difficult to learn French well. [ ]
A. that
B. it
C. if
D. it is
答案:B
编制推焦顺序时应考虑哪些因素?
飞机请求立即强迫着陆的辅助联络信号是()
A、飞机通过跑道上空,昼间放下起落架,夜间打开着陆灯
B、飞机通过跑道上空,昼间摇摆机翼,夜间打开着陆灯
C、飞机通过跑道上空并发出一颗或者数颗信号弹(昼、夜间相同)