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 george will.
b. as jake was reading the email from june yet again, the flight attendant coughed gently to get his attention.
c. i simply cannot make heads or tails of rap lyrics, but i suppose i'm just too old to understand them.
d. i would like to visit the kinshasa, but i understand the city is unsafe for foreigners.