Write a multi-choice question for the following article: Article: While your pet fish may appear to be ignorant of your presence, chances are that it knows you extremely well and can probably even identify you from a crowd of human faces! At least, that is the conclusion reached by scientists the University of Oxford in the U.K. and the University of Queensland in Australia, following an extensive study of the archerfish , a species of tropical fish that can be found all the way from India to Indonesia, the Philippines, and Australia. The ability to distinguish between human faces is a complex task. That's because we all have the same basic features -- two eyes sitting above a nose and a mouth. It's only the subtle differences that make humans distinct from one another. Since this requires a combination of both visual sense and memory, researchers had always assumed that _ was a skill possessed only by those with complicated brains, i.e., humans, a few select animals -- such as horses, cows, dogs, monkeys and some birds, like pigeons. To test if this assumption was accurate, a team of scientists led by Dr. Cait Newport, Marie Curie Research Fellow in the Department of Zoology at Oxford University, decided to study fish. The aquatic animals have small brains that lack the neocortex , or neocortex-like structure, believed to help recognize the subtle differences between human facial features. The team began by presenting four archerfish with images of two human faces. Initially, the fish spat randomly at both. However, they soon learned that pouring water at the one selected by the researchers earned them a food treat. After that, they focused primarily on that image. The researchers then took the experiment one step further, by introducing 44 other human faces to the mix. To the researcher's astonishment, the trained archerfish were able to recall the learned image almost 81% of the time. And this accuracy improved to 86% when the researchers made the identification even harder, by replacing the colored photos with a set of black and white images and hiding the shape of the head.
Question: In the experiment, the researchers trained the archerfish _ .Options:A by taking photos of fishB by improving people's imagesC by rewarding them with foodD by covering their headsAnswer:C