Question
I have a project to due and i don't know what fertilzer to
use?
What to start with a plant or seed?
i need help

Answer
Seeds take time to germinate.  Do they take more time if you fertilize them?  That's a good research question.  So far, all evidence points to 'no'.  If you don't have a project plant, this is a possible subject to investigate.  Radish seeds sprout very quickly and would be good to use for something like this.

Does the right fertilizer build bigger Radishes?  This is another discovery you can show.  I'll tell you how if this sounds interesting.  It's easy to see if Radishes from Group C are the biggest Radishes or Radishes from Group D are the smallest.

Please give me more details about your project.  Sounds like fun!