Questão de Língua Inglesa

Some words in English have different forms and spellings according to the country where the variety is spoken. For example, we can infer that the teenager who owns this blog is British because he uses the word holidays for vacation. Look the list of words below and decide if the difference in spelling is related to language variation or if it is a mistake. I. collor = color II. humour = humor III. realise = realize IV. centre = center