第二部分：知识运用（共两节, 满分35分）
第一节单项填空（共15小题；每小题1分，满分15分）
请认真阅读下面各题，从A、B、C、D四个选项中，选出最佳选项,并在答题卡上将该项涂黑。
It is believed that ______ European chemist called Felix Hoffmann first produced ASA which completely changed ______ man’s understanding of aspirin.
A. an; a                        B. the; a                       C. a; /                          D. an; /