Ella no creía que Pedro hacer eso.

pudieras
puede
pueda
pudiera

If possible, please explain how you chose which tense to use

Ella no creía que Pedro pudiera hacer eso. I don’t know how to explain it but I speak fluent Spanish and we would use PUDIERA in that sentence!

For this question, it will be important to use the words "mejor" (better), "lo mejor" (the best), and "lo peor" (the worst). while "mejor" is comparative (you are comparing one thing to something else), "lo mejor" and "lo peor" are superlative (there is nothing else better or worse than what these words are describing - there is no comparison).  you could say something like: la música rap es mejor que la música clásica - que es lo peor - pero la música rock es lo mejor de todas las formas de la música (rap music is better than classical music - which is the worst - but rock music is the best out of all the forms of music).