The word "must" is the correct answer because it expresses a strong probability or logical conclusion. In this context, it implies that it is expected or necessary for the person to feel exhausted after running 20km as part of their marathon training.

The word "must" is used in this context to express a strong likelihood or certainty. By saying "You must be very happy," the speaker is implying that it is highly likely or almost certain that the person is feeling happy because they passed their driving test.

The correct answer is "might" because the speaker is unsure of Steven's whereabouts and suggests the possibility that he might be in a meeting. The use of "might" indicates uncertainty or possibility in this context.

The word "might" is the correct answer because it suggests the possibility or likelihood of the person wanting to borrow the book. The speaker is expressing their assumption or belief that the other person might be interested in borrowing the book instead of buying it.

The speaker is stating that the bag cannot be Jane's because her bag is black. This suggests that the bag in question is a different color, leading to the conclusion that it cannot belong to Jane.

The correct answer is "can't". This is because the speaker has just seen Marilyn in town, contradicting the statement that Marilyn and Bob are on holiday in Sicily. Therefore, it is not possible for them to be on holiday in Sicily.

The correct answer is "can't". In this conversation, the speaker expresses disbelief or surprise at the idea of the person getting married. The word "can't" is used to show that the speaker doesn't believe it to be true or serious.