D. She says to Gatsby that, "You always look so cool."
Explanation:
This event happens in chapter seven. Nick and Gatsby are visiting the home of Tom and Daisy, and we learn that it is an extremely hot day. While the group decides what to do for the evening, Daisy suggests that they go into town. At that moment, Gatsby's and Daisy's eyes meet, and she tells him that he always looks "cool," like a man in an advertisement. They all witness the scene, and this leads Tom to believe that Daisy is in love with Gatsby.
