答案：B

题目分析：考查虚拟语气用法。本题考查的是if条件从句与过去事实相反的虚拟语气，故从句用had + v-ed，主句用would / could/ should / might + v-ed。句意：如果Dewey先生在场的话，他会提供那里人们的任何可能的帮助。故B正确。

【知识拓展】

1. 表示与现在事实相反或不可能发生：条件状语从句：一般过去时（虚拟语气中be→were）主句用：would(should, could, might)+动词原形。

If we had time now, we would read it again.

If I were you, I would work hard.

2. 表示与过去事实相反或不可能发生：条件状语从句：had+过去分词；主句：would(should, could, might)+have+过去分词。

If I had known your telephone number then, I would have called you.

3. 表示与将来的事实可能相反或不可能发生：条件状语从句：①一般过去时②should +动词原形③were to+动词原形；主句：would(should, could, might)+动词原形。

If it should rain, the crops would be saved.