Cell result is based on the drop down selected

Hi Everyone,

I am quite new in this forum and so far I find this forum very helpful to me. However since it's been a while since I attended an excel refresher, and now I am having challenges in formulas.
So here's what I'm trying to do.

I created a dropdown list in column B (Volume). Under column C, I would like the authors of the book to be populated based on the selected number of volume. Hence, an author could be assigned to one or more volumes. My vlookup formula seem to work fine but this will work if the formula is saved on the whole column. I need to know how I can populate the authors upon selection of the volume.

I thank you all in advance.