The correct option is D therefore
In the sentence, one clause or idea, "we went to see the movie instead" is the consequence of another "the magic show was cancelled".
Option D: 'Therefore' is a conjunction used in inference-based sentences, or to indicate the consequence of an action. The word itself means 'for that reason, consequently'. Hence this is the most suitable option.
Option A: 'But' refers to contrast, for example, 'She is obedient but her sister is disobedient.' The given sentence focuses on consequence rather than contrast.
Option B: 'And' refers to an addition. It merely connects two sentences that do not affect one another. It isn't relevant here as one sentence (or clause) is the result of the other.
Option C: 'Since' refers to reason or cause. It does not refer to the consequence, but to the reason behind doing something. The meaning isn't relevant here.
Hence options A, B and C are incorrect.