The correct option is C would
Here, 'would' is correct because it is used for describing a possible action or event that did not in fact happen, because of something else. Here, piano lessens 'did not happen' because of not having more time.
'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.
'May' is incorrect because it is used to say that something is possible.