29.下列何者的導管穿過頰肌(buccinator),開口於上排第二臼齒的口腔前庭(vestibule)?(A)腮腺(parotid gland)(B)下頜下腺(submandibular gland)(C)舌下腺(sublingual gland)(D)腭腺(palatine gland)