Select the most appropriate option to fill in the blank.

You are well prepared to handle the responsibilities bestowed ______ you.

upon

The correct option to fill in the blank is upon.

The word "bestow" means to give or grant something to someone as a gift or privilege. So, the responsibilities were given to you as a gift or privilege. The word "upon" is used to indicate that something is happening to someone or something else. In this case, the responsibilities are happening to you.

The other options are not as appropriate. The word "to" is used to indicate movement towards something. The word "for" is used to indicate a purpose or reason. The word "at" is used to indicate a specific location. None of these options make sense in the context of the sentence.