When adjusting a magnetic compass using the fore-and-aft permanent magnets，you should（）.
- Ause the magnets one at a time，putting one in one side and then one on the opposite side，one step higher
- Buse the magnets in pairs，starting at the top，with trays at the highest point of travel
- Cuse the magnets in pairs，from the bottom up，with the trays at the lowest point of travel
- Dfill all the trays with magnets，then remove them one-by-one until the deviation is removed