Answer:
A. Securely
B. "...no way in the world can you get rid of the nasty hard thing..."
Explanation:
A. The word fast in this context means securely. For example, if I held my money fast it would mean that I clutched it tightly to make sure nothing could happen to it.
B. This quotation shows that the harness was held securely on the horse, since he couldn't get it off.
Dioneo's role as the narrator of the "Tenth Day: Tenth Tale.", he tell this particular tale to the other members of the brigata and it reveal about his character of recognizing the gender hierarchy in society and focuses most of his life’s work exploiting the tensions that result.