Which of the following causes opening of Eustachian tube?
The Eustachian tube/auditory tube in the adult is 36 mm in length. (Range 32-38 mm) From its tympanic end, it runs downward forward and medially joining an angle of 45° with horizontal. 
In infants, the tube is shorter, wider and is more horizontal.
It has two parts—a pharyngeal cartilaginous part which forms 2/3rd (24 mm) of its length (i.e. inner or medial part) and a tympanic bony part which forms remaining 1/3rd (outer or lateral part) (12 mm). This is just reverse of external auditory canal
The two parts meet at isthmus which is the narrowest part of tube.
The fibers of origin of tensor palati muscles are attached to lateral wall of the tube. Contraction of this muscle during swallowing, yawning and sneezing opens the tube and this helps in maintaining equality of air pressure on both sides of tympanic membrane. Contraction of levator palati muscles which runs below the floor of cartilaginous part also helps in opening the tube.
It is lined by pseudostratified columnar ciliated epithelium (cartilaginous part contains numerous mucous glands).

Ref. Dhingra 6/e, p 57, 5/e, p 63
Salpingopharyngeus
Levator veli palatini
Tensor veli palatini
None of the above