Answer:
A. Spontaneous concerts and other spur-of-the-moment events are easier to organize nowadays now that e-mailing, texting, and social networking get information to people instantly.
Explanation:
A complex sentence is formed by an independent clause and a dependent one. That means we need to transform one of our clauses into a dependent/subordinate clause to obtain a complex sentence.
The best option is letter A. The first clause remained the same, which makes it now the main clause. The second clause begins with "now that", which is a subordinate conjunction. We have here a complex sentence.
Letters B and C joined the clauses correctly, but did not form a complex sentence because both clauses remain independent.
Letter D could have been a good option, but both sentences were transformed into subordinate ones. If you read the sentence, you'll notice it does not make sense because of the "although" that was added to it.
