【题目】As we know, his father is a very famous scientist in physics. But what you don't know is that he _______ as a farmer for five years.
A.has worked
B.worked
C.had worked
D.works

【答案】B
【解析】句意：众所周知，他父亲是物理方面的著名科学家，但是你不知道的是他当了5年农民。此处指的是他父亲曾经是一个农民，应该用过去式。故选B。