Which of the following is a complex sentence?
a. Check out the editorial page in today's paper and you'll notice the piece by Oscar Lewis.
b. As Jake was reading the letter from June yet again, the flight attendant coughed gently to get his attention.
c. I would like to visit the Kinshasa, but I understand the city is unsafe for foreigners.
d. I simply cannot make heads or tails of rap lyrics, but I suppose I'm just too old to understand them.