Answer:

Explanation:
To determine the most suitable conjunction to complete the sentence, we need to consider the relationship between the two clauses.

Contrasting Relationship:
Option 'A' (but) is a conjunction that indicates a contrasting relationship between two ideas. It is used to show a contrast or opposition between the cancellation of the magic show and the decision to see a movie instead. However, in this context, there is no indication of a contrast between the two actions.

Adding Relationship:
Option 'B' (and) is a conjunction that indicates an addition or continuation of ideas. It is used to connect two similar or related actions. In this context, using 'and' would imply that the decision to see the movie was an additional event that happened simultaneously with the cancellation of the magic show. However, the sentence implies that the decision to see the movie was a result or consequence of the cancellation.

Cause and Effect Relationship:
Option 'C' (since) is a conjunction that indicates a cause and effect relationship. It is used to show that one action is the result or consequence of another action. In this context, using 'since' would imply that the cancellation of the magic show was the cause of the decision to see the movie. However, there is no clear reason given in the sentence to suggest that the cancellation directly caused the decision.

Conclusion Relationship:
Option 'D' (therefore) is a conjunction that indicates a conclusion or result. It is used to show that one action is the logical consequence or result of another action. In this context, using 'therefore' correctly conveys that the cancellation of the magic show led to the decision to see the movie instead. The cancellation can be seen as the reason or cause for the change in plans.

Therefore, the most suitable conjunction to complete the sentence is 'therefore'.