【单选题】____ radar is to airplanes and ships, ______ eyes are to human's body.
【单选题】In restricted visibility the speed of a vessel without operational radar may be ________ enable effective avoiding action to be taken on sighting another ship.
【单选题】My radar is not working.I require shorebased radar assistance.Is shorebased radar assistance ________ ?
【判断题】The welfare service in Britain only provides allowances and pensions for those jobless and retired people.
【判断题】有理数域 Q 是 R(i) 的真子域, R(i) 是实数域 R 的真子域, 实数域 R 是复数域 C 的真子域.
【判断题】复数域存在既不是有理数域, 也不是实数域的真子域.
【单选题】_____ radar is to air plane and ships, _____ eyes are to human body.