6 Complete the sentences with must, might or can't. 1 This ring ... be gold -it only costs £1.99! 2 lt ... be my book- it's got my name in it. 3 David isn't at school today. He ... be ill, but perhaps he's on holiday 4 Alison's got lots of cats. She ... like them. 5 They ... be from Yakutia, but I'm not sure. 6 He ... be scared of heights - he went climbing in the Pyrenees last year.