3. 【解析】选B。细节理解题。根据第三段的第一句话“During World WarⅡ，Pauling was a member of the Research Board for National Security，for which he was awarded the Presidential Medal of Merit in 1948. ”我们可以得出正确答案为B选项。
4. 【解析】选B。主旨大意题。本文主要介绍了Linus Pauling一生的成就及其对世界的贡献，所以应该选择B选项。
