Les just bought a megaphone of root beer. as he drinks from the giant cup, he eventually becomes full. one of his friend's comments, "if you don't stop drinking that stuff, you will get sick." les replies, "hey, i bought it, and i am not going to waste one drop of it." les's behavior could best be described by which of the following mental biases:

The correct answer is - the sunk cost fallacy.

Explanation:

The sunk cost fallacy is phenomenon that is occurs when individual continue their behavior or action because of the prior investment of time, money or effort.

Lee's behavior is best example of the this fallacy or biases which is related to the aversion of the loss of money that can be seen as mental bias due to her ongoing commitment of finishing the drink she bought.

Thus, the correct answer is -  the sunk cost fallacy.