Cilia are located in the:

Cilia are tiny, hair-like structures that play a crucial role in the respiratory tract. They are found lining the surfaces of the airways, such as the trachea and bronchi. Their primary function is to help move mucus and trapped particles out of the respiratory system toward the throat, where they can be swallowed or expelled. This mechanism is an essential part of the body's defense system, as it helps keep the airways clear of contaminants and pathogens, thereby supporting overall respiratory health.

In contrast, while the urinary and circulatory systems do have mechanisms for the movement of substances, they do not rely on cilia. The digestive tract has a different type of movement through smooth muscle contractions rather than the action of cilia. Thus, cilia are specifically associated with the respiratory tract, making it the correct answer.