单选题 .  The extent and limits of ape (猿) intelligence is a hot area in science, but most of the research has focused on cognition. Now a team of scientists has turned the spotlight on emotions, and how well apes can read the human kind as displayed in our facial expressions.
    A paper in the September issue of the journal Developmental Science describes studies from the Wolfgang Kohler Primate Research Center in Leipzig, Germany. In the first test, a researcher sat at a table on one side of a panel while an ape sat on the other side. Two opaque boxes rested on the table. The scientist opened one box  (making sure the ape could not see inside) and smiled with pleasure. He next opened the other and made a disgusted face. The ape was then allowed to reach through one of the holes in the panel and pick one box. Which would he choose?
    In 57 percent of the tests, the ape chose the box that elicited a smile from the scientist rather than an expression of disgust. Good choice. The box that brought the smile contained a grape, and the ape was rewarded for his perspicacity (敏锐) in reading human facial expressions. The other box contained dead insects. The apes' skill at reading an expression of happiness indicates that they can read meaning in the emotional expressions on human faces, suggesting that despite 6 million years of separate evolution apes and humans share a common emotional language.
    In the next experiments, the set-up was the same. An ape saw the scientist hold up a grape and a slice of banana, but his view was then blocked as the scientist put one treat under one cup and the other under the other cup. The ape then watched as the scientist looked under each of the two cups in turn, making an expression of happiness at one and of disgust at the other. The scientist next reached under one cup  (at this point, the ape's view was again blocked, so he could not see which cup the scientist chose) and ate what was inside. His view restored, the ape saw the scientist chewing something with pleasure, and then was allowed to choose a cup for himself.
    This time the apes tended to choose the cup that had triggered the expression of disgust. Counterintuitive (违反常理的)? Not at all. The apes went beyond the far too simple "pick cup that elicited happy face" to make a fairly sophisticated computation. That is, they seemed to reason that the human would eat the food that made him smile, emptying that cup, with the result that only the disgust-inducing cup would still contain a snack.1.  The research on ape emotions is aimed at understanding ______.