C

Clinical studies show that without any magnification the MB2 orifice is found only in about one-quarter of maxillary molars (18 %–25 %) [Buhrley 2002, PMID 12043874; Vasundhara 2017, PMID 29279624]. This figure is closest to the 30 % range offered in the choices, making 30 % the best answer.