Select the most appropriate option to fill in the blank.

Thus, ______ of their purpose, the three knights tried another plan.

foiled

The most appropriate option to fill in the blank is foiled.

The sentence is about the three knights who were trying to achieve a purpose, but were unsuccessful. The word "foiled" means to prevent or defeat someone or something from achieving their goal. It is the most appropriate word to use in this context because it describes how the three knights were prevented from achieving their purpose.

The other options are not as appropriate.

• Involved means to be connected with something or someone. This does not make sense in the context of the sentence because the three knights were not connected with their purpose, they were trying to achieve it.
• Toiled means to work hard or laboriously. This does not make sense in the context of the sentence because the three knights were not working hard, they were unsuccessful.
• Failed means to not succeed in doing something. This is a possible option, but it is not as specific as "foiled". "Foiled" specifically describes how the three knights were prevented from achieving their purpose.