Read the following advertisement and mark the letter A, B, C, or D on your answer sheet to indicate the option that best fits each of the numbered blanks from 1 to 6.

SHEEP CAN RECOGNISE FACES!
Many people think sheep aren't very ___(1)___ creatures. But in fact, according 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 ___(2)___. However, it seems that sheep are also social animals that can recognise other sheep as well as familiar humans. In experiments, researchers trained eight sheep to recognise the faces of celebrities from photographs. Training involved ___(3)___ the sheep to make decisions about the photos ___(4)___ they saw. At one end of a room, they would see two different photographs, and would receive a reward of food ___(5)___ 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!