Final answer:
A complex sentence is a sentence that contains an independent clause and at least one dependent clause. The sentence 'Although I am here, I don't feel ready for the game' is a complex sentence.
Step-by-step explanation:
A complex sentence is a sentence that contains an independent clause and at least one dependent clause. An independent clause is a clause that can stand alone as a complete sentence, while a dependent clause cannot. In the given options, the sentence that is a complex sentence is Option D: Although I am here, I don't feel ready for the game. This sentence has an independent clause 'I don't feel ready for the game' and a dependent clause 'Although I am here.'
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