It was ____ very rare find and the archaeologist who made ____ discovery said it was like unearthing a

Mona Lisa. [ ]

A. a; the

B. the; the

C. the; a

D. a; a

试从生油母岩类型、油气生成的动力因素、油气生成的阶段等方面论述干酪根晚期热降解成烃理论的基本特点。