The lining of the respiratory tract is lined by filamentous structures known as cilia. The cilia are the brush like like structures, which help in the movement of the mucus and other unwanted particles out of the respiratory tract.
The cilia help these particle to move in opposite direction, that is from lungs to nostrils. In case, the cilia is absent it can cause congestion due to the accumulation of the mucus in the respiratory tract.
So, the correct answer is cilia.
