Образовать множественное число: boot , ox, fox, wom¬an, mouth, mouse, goose, deer, ship, sheep, crisis, nucleus, formula, room-mate, man-of-war, boy-messen¬ger, passer-by.

boot - boots ox - oxen  fox - foxes  woman - women mouth - mouths mouse - mice  goose - geese  deer - deer  ship - ships sheep - sheep crisis - crises nucleus - nucleuses formula - formulae  room - rooms  mate - mates  man-of-war - men-of-war  boy - boys messenger - messengers passer-by - passers-by