Weilin Chen is sitting in a class that precedes lunch. His stomach begins to rumble and grumble. Instead of thinking about the day's lecture, Chen begins to think about lunch and his choice of places to eat. He even begins to narrow down the selection of foods that he might want for lunch. Chen is focusing on biological needs that are at present unfulfilled and have produced what might be thought of as an unpleasant state of arousal. Which of the following theories best describes Chen's experience? （ ）