Упр. 2. Напишите следующие слова a) во множественном числе: a house, a mouse, a potato, a piano, a dish, a baby, a valley, a knife, a roof, a woman, a tooth, a child, a box, a brother-in-law, a boy, a toothbrush, a workman, a classroom, an armchair, a matchbox, a bookshop, a woman-teacher, a secretary, a nurse, a stepmother, a wife, a grown-up, a formula; b) в единственном числе: feet, sheep, teeth, boxes, libraries, babies, needs, theses, data, heroes, kisses, families, sisters-in-law, watches, actresses, saleswomen, boyfriends.