Вопрос по английскому языку:

В ответах на это задание говорят, что мы должны поставить артикль "a" под номером 10. Подскажите пожалуйста, почему? Речь же идет о конкретном петухе, который гуляет.

1)… Frenchman was once travelling in (2)… England. He did not know (3)… English quite well. He could speak only (4)… little. One day he was eating in (5)… small pub and he wanted to order (6)… eggs. But he didn’t know (7)… English word for (8)… eggs. Suddenly through (9)… window he saw that (10)… rooster (петух) was walking in (11)… yard. He asked (12)… waiter what was the English for (13)… “roster”. (14)… waiter told him. (15)… Frenchman then asked what was the English for (16)… “rooster’s wife”. (17)… waiter told him that it was (18)… hen. Next (19)… Frenchman asked what was the English for “hen’s children”. (20)… waiter told him that they were (21)… chickens. (22)… Frenchman asked what (23)… chickens were before they were born. (24)… waiter told him they were (25)… eggs. “You’ve explained everything very well,” (26)… Frenchman said. “Please bring me two (27).… eggs and (28) … cup of (29)… coffee.”