Select the most appropriate option to fill in the blank.

He is both diligent ______ efficient.

and

The correct option to fill in the blank is and.

The sentence is about the person being both diligent and efficient. The word "and" is the most appropriate word to use because it connects the two adjectives. It is the most appropriate word to use in this context because it describes how the person possesses both qualities.

The other options are not as appropriate.

• Also means "in addition to". This is a possible option, but it is not as strong as "and". "And" specifically connects the two adjectives.
• But means "on the other hand" or "however". This is not a possible option because it does not make sense to say that the person is both diligent and efficient, but not efficient.
• Yet means "nevertheless" or "despite that". This is not a possible option because it does not make sense to say that the person is both diligent and efficient, yet not diligent.