At last John Smith stepped down as the company's CEO and returned to his roots in software research.

A. retired

B. resigned

C. revived

D. Reacted

【答案解析】本题正确选项B。【译文】最后，约翰·史密斯辞去了首席执行官的职务，回到他以前的软件研发工作中去。【解析】砗个备选项中，A项retire“退休”；B项resign“辞职”；C项revive“复活，苏醒”；D项react“作出反应”。题中画线词step down“辞职，走下”和resign意思最接近，因此，依据题意本题最符合题意的选项为B。