Respuesta :
The clause that the writer should add to the end of the sentence in order to create a complex sentence is "if we have free time in the afternoon".
What is a complex sentence?
One independent clause "and at least one dependent clause" make up a complex sentence.
The abovementioned clause can be used to create a complex sentence as a subordinating conjunction "if" is used in the clause which is making it a dependent clause as it will be providing a reason to the main clause.
Hence, the correct option is C that is "if we have free time in the afternoon".
To learn more about complex sentences here
https://brainly.com/question/528783
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