A、It is too expensive. B、It is not precise. C、It is dangerous. D、It is time-consuming. D讲话人在原文中提到，只要有可能，他们就会使用直升机来帮助他们绘制冰面地图和寻找合

As we all know, cruising in the Southern Ocean isn’t always plain sailing. But as it is becoming important to find better ways of navigating safely and avoiding future collisions because of increasing visitor ships, the Antarctic Polar View project is using satellites to map the sea ice to help ships find the best way in the vast white continent. There are very large lumps of heavy ice in the water which might look beautiful, but I believe you do not want to hit it with a ship, because if it happened your ship would be damaged. Therefore, navigating through it is an important problem, not only in terms of the safety of the ship, but also in terms of the speed of the ship, and the efficiency of the ship. You could have another choice—take a quicker and cheaper route rather than spending an excessive amount of time going through an area of very thick ice. The quickest way to travel is to clear water channels, but it is a difficult task to find these routes.
    The area we’re dealing with is absolutely enormous. The only way of monitoring that area of ocean effectively is by using satellites. Therefore, we use a satellite named NVSAT, which is a satellite that collects information and picks up differences in ocean surface roughness and that helps us to see the difference between open water and the sea ice.
    Radar allows the Antarctic team to see straight through the clouds down to the surface of the sea. With detailed images, it’s even possible to see cracks in the surface which can lead to dangerous ice falls. Wherever possible we would use helicopters quite a lot and put them up in the air to map the ice and look for where we might find what we call leads, you know, which are large areas of clear water that the ship might be able to move through. But it is certainly a much more difficult and time-consuming operation.
    OK. That’s all for today’s talk. Next time, I will share with you more about this mapping project. Thank you!
    Questions 23 to 25 are based on the recording you have just heard.
    23. What is the Antarctic Polar View project about?
    24. Which is a major function of the satellite named NVSAT?
    25. What is the disadvantage of using helicopters to help map the ice?