一、单项填空（共 15 小题；每小题 1 分，满分 15 分）
从 A、B、C、D 四个选项中，选出可以填入空白处的最佳选项。
1. We all felt puzzled by the ______ answer he gave.
A. generous B. ambiguous C. curious D. concrete
2. Among so many scientists in this field, he ______ and achieved great success.
A. stood out B. stood for C. stood aside D. stood by
