This is the 5784th most frequent Chinese word.
呼吸系統
Respiratory system.
In this sentence, '呼吸系統' (respiratory system) is used as the subject to indicate its significance in body anatomy.
呼吸系統是人體的重要部分。
The respiratory system is an important part of the human body.
Here, '呼吸系統' (respiratory system) is part of a conditional clause describing a scenario of health issues caused by infections.
如果呼吸系統受到感染，會影響健康。
If the respiratory system gets infected, it will affect health.
In this sentence, '呼吸系統' (respiratory system) is the object of the action, related to its functionality improvement through exercise.