42 恆牙上顎第一大臼齒的斜（oblique ridge）走向為何？ (A)近心頰側牙阜（mesio-buccal cusp）之舌側牙阜到近心舌側牙阜（mesio-lingual cusp）之頰側牙阜 (B)遠心頰側牙阜（disto-buccal cusp）之舌側牙阜到遠心舌側牙阜（disto-lingual cusp）之頰側牙阜 (C)遠心頰側牙阜（disto-buccal cusp）之舌側牙阜到近心舌側牙阜（mesio-lingual cusp）之遠心側牙阜 (D)近心頰側牙阜（mesio-buccal cusp）之舌側牙阜到遠心舌側牙阜（disto-lingual cusp）之頰側牙阜