Select the most appropriate option to fill in the blank.

Please sit down and have breakfast _______ us.

with

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

The word "with" is a preposition that indicates that something is done in the company of someone or something else. In this context, it makes sense to say that the person should sit down and have breakfast with us, as we are the ones who are inviting them to have breakfast.

The other options are not as appropriate. The word "to" is a preposition that indicates movement towards something. This does not make sense in the context of the sentence, as the person is not moving towards us, they are sitting down with us. The word "at" is a preposition that indicates a specific location. This does not make sense in the context of the sentence, as we are not referring to a specific location, we are simply inviting the person to have breakfast with us. The word "on" is a preposition that indicates that something is placed on top of something else. This does not make sense in the context of the sentence, as we are not placing the person on top of us, we are inviting them to have breakfast with us.