Нужно множественное число A pin, a hat, a fox, a baby, a day, potato, a volcano, a piano, a photo, a knife, a roof, a half, a leaf, a cliff, a chief, a life, a family, a queue, a bath, a berry, a valley, a century, a salmon, a taxi, a person, a penny, a watch, a virtuoso, a lily, a woodworm. 14 B. A man, a woman, a German, a foot, a tooth, a sheep, a ship, a fish, an ox, a fox, a child, a fireman, a mouse, a swine, a house, a louse, a goose, a mongoose, a deer, a means, a series, a species, an aircraft, an offspring, a Swiss, a Japanese, a Maltese, a Portuguese, a Chinese, a Milanese. C. A passer-by, a mother-in-law, a room-mate, a forget-me-not, a merry-go-round, a fellow- worker, a man-of-war, a school-inspector, a commander-in-chief, a boy-messenger, a personnel-manager, a woman-driver, a man-servant, a hanger-on, a face-lift, a spoonful, a cupful, a boyfriend, a grown-up, an office-block, a workmate.