Read the text and chose the correct answer for the following questions.

A very clever family

The Smiths are possibly the cleverest family in the country, and now the youngest member, ten-year-old Charlotte, has won a national spelling competition to add to the family's successes. Charlotte is the youngest ever winner of the National Young Spelling Bee Competition – the youngest winner before her was her older sister, Helen, who won it when she was eleven. Charlotte and Helen's older brother, Mark, is also very clever. He finished school early and went to university at the age of fifteen, three years before most young people start their university studies. The children's parents, Charles and Vivien, are both teachers and say their children's success comes from working hard, playing hard, and following strict rules about homework and bedtimes. “Other people think that Charles and I don't let the children have any time to relax and play and that we're always making them do their homework. But it's not true!” says Vivien. “We have lots of fun time in the family. But there's a time for fun and there's a time for work, and we make sure the children understand that work comes before play.” When Charlotte took part in the spelling competition, the whole family, including her grandparents, went to watch her. Helen took off a day from school – the first day in her life that she missed going to school. “I felt bad about missing school,” Helen said, “but I think it was important to Charlotte that I was there.”

You _______ arrive at work on time or you may be fired. A. must B. has to C. mustn't D. can