Mark the letter A, B, C, or D on your answer sheet to indicate the correct option that best fits each of the numbered blanks from 19 to 24

Many people think sheep aren’t very intelligent creatures. But in fact, ___(1)___ to new research, they may be cleverer than we think. For example, sheep can actually be trained to recognise human faces from photographs!
Recognising faces is an important human social ___(2)___. However, it seems that sheep are also social animals that can recognise other sheep as well as ___(3)___ humans. In experiments, researchers trained eight sheep to recognise the faces of celebrities from photographs. Training involved getting the sheep to ___(4)___ decisions about the photos they saw. At one end of a room, they would see two different photographs, and would receive a ___(5)___ of food for approaching the photograph of the celebrity; if they approached the wrong photograph, they got nothing. Over time, they learned to ___(6)___ getting food with the celebrity’s photograph. And after training, the sheep correctly chose the celebrity’s face eight times out of ten!