The right answer is C.
Synovia is a viscous biological fluid located at the joints and fulfilling several functions. It limits bone friction between them, dampens shocks, provides the nutrients and dioxygen necessary for chondrocytes (cartilage cells) while eliminating their metabolic waste, and benefits from the presence of immune cells to eliminate possible body foreigners.
The correct answer for this question is letter C. Epiglottis is the one who prevents food from entering the trachea. It moves in a back and forth manner. When a person swallows, it covers the entrance of the larynx by flattening itself backwards.
Encyclopedia of cell biology, molecular biology of the cell
