'Source' is correct. I hope these sentences give you an idea of how source is chosen over resource. 'This is a good source of information' 'I used various sources for this information' 'This information came from an unknown source' 'This website is the source of all my information' Whereas you could say 'The internet is one of my resources' 'We have many resources for acquiring knowledge' So I would simply put it as, using 'source' is more specific and is singular, whereas using 'resource' is still right but implies it might not be the only one. I hope this made sense & was helpful.

Hello! "source" also means "a cause", "a way" ( you know/get something thanks to it) So, I think "i use the website. This source is helpful) # " natural resources"