Question

Which form of the modifier correctly completes the sentence?

Answer 1

B. Better 
The other ones wouldn't be considered proper grammar in this case. Wish I could explain it more but I don't know how. I can use examples to show when 'well' would be used correctly. Best is more of a word that can be used to modify an adjective. For example: "That is the best apple pie!"
For 'well', I would use it more for describing a feeling or how you did something. So if you were to kick the football really hard, you would say, "I just kicked that football really well." Or it you were using it as a feeling, you could say "I am doing well". Hope this helps...