Which of the following is a complex sentence? a. as jake was reading the email from june yet again, the flight attendant coughed gently to get his attention. b. i would like to visit the kinshasa, but i understand the city is unsafe for foreigners. c. check out the editorial page in today's paper and you'll notice the piece by george will. d. i simply cannot make heads or tails of rap lyrics, but i suppose i'm just too old to understand them.

A complex sentence is a sentence which contains both an independent and a dependent clause. Having this in mind, the only correct answer is A. As Jake was reading the email from June yet again, the flight attendant coughed gently to get his attention.
Here, the first part of the sentence (up until the comma) is dependent, and the other part following the comma is independent. The other sentences do not have such a structure - all of them are compound, not complex sentences, given that they consist of at least to independent clauses, with no dependent ones. 

Dogs have been considered man’s best friend for decades! most likely because of their kind and loyal nature. they make splendid companions. their loyalty is beyond compare and after all, a dog is the only thing on earth that loves you more than he loves himself! dogs see us as their friends and leaders, they’ll do anything in their power to ensure your comfort and safety.