Puppy Petey once told his mother that he wants a boy for Christmas. His mother promise to him that she will find a boy for Petey if he'll be a very good puppy. The day before Chritmas Petey told his mother that he was a well-behaved puppy. In truth, almost well-behaved. Then Petey's mother went outside to look a boy for him. But it appeared that there is no a free boy for Petey. Petey's mum advised him to ask others dogs if one od them can give him his boy.
Ну тут как посмотреть. Если говорящий имеет в виду долг или обязанность, то must. Если он выражает принуждение что то сделать, то have to. Ну а если просто говорит " тебе следует", то should. Но я бы предпочла must.
1) Which is the longer river? C. 2)Which is the highest mountain? b 3)Which is the biggest country in the world? c 4)Which is the largest lake in Africa? d