How many dummy variables can I use

[sansan]

Hi, I'm working on my first econometrics project. My topic is on the impact of foreign direct investment on economic growth (as GDP). Panel data analysis, 10 countries, and 20 years. When I got my proposal's feedback, my professor suggested that I include dummy variables. He wrote: country dummies 9, and year dummies 19. My question is: can I include BOTH dummies? I asked another professor, and he told me that I could only use one dummy, that I couldnt' include both of them. Please and answer will be highly appreciated.

Thank you!

[startz]

Using both should be fine.

[sansan]

Oh thank you so very much!!