A:had enjoyed
B:enjoyed
C:have enjoyed
D:was enjoying
I'll give a talk tomorrow. I'm thinking about _______.
材料一: 在北京人生活的洞穴里,用火遗迹十分集中。灰烬堆积很厚,最厚处有6米。
材料二:“上古之世……民多疾病。有圣人作,钻燧取火以化腥臊,而民说之,使王天下,号之曰燧人氏。” ——《韩非子》
请回答: