为了解身边的生物，我们可以通过______法，记录下所看到的生物和它们的生活环境；为了搞清楚光对鼠妇生活的影响，可以通过______法进行探究，其变量是______．

---Larry, could you please tell me ___________?

---Sure. In the post office on Bridge Street.

A．where you bought the stamps

B．where did you buy the stamps

C．when you bought the stamps

D．when did you buy the stamps