adding chemical system的用法和样例：
- Real ants communicate with each other by a chemical system called pheromones.
- The chemistry of the effects of light on chemical systems.
- Latter-day agriculture had walked along oil agriculture, crossbreeding to add chemical fertilizer, insecticide and herbicide a few large stage.
- Several techniques which can en hance coagulation, such as adding chemical feed machine, changing the method of chemical feed, improving the influent mode, are brought up.