The correct option is D would
Here, 'would' is correct because it is used to give advice. Here, it is being adviced that if I 'were' you, I would take a bus.
'Shall' is incorrect because it is used in questions with I and we for making offers or suggestions or asking advice.
'Can' is incorrect because it is used to say that it is possible for somebody/something to do something, or for something to happen.
'Will' is incorrect because it is used for talking about or predicting the future.