The use of trigonometry(三角学) to describe the electrical signal has proved very valuable for engineers.
举一反三
- The _________ of mental disorders has proved to be very difficult.
- The use of electrical appliances has been quite popular in the Western world.
- Wide use of the Internet has made _____dating very popular.
- the use of signal
- a fixed signal that lets engineers know if a train can enter a block. A: ABS (automatic block system) B: lock C: lock signal